Okay just checked out. Heavy mixed feelings about this property...

tl;dr: Only stay here on Sunday-Thursday nights if you enjoy sleeping at reasonable times for reasonable hours, or if you're a hard partier/clubber that will be out clubbing until 3am on Fridays and Saturdays.

Made a four night booking from Oct 11th to Oct 15th (Friday -> Tuesday), on cash via Long Term Stay rate for a total of 633.10 euros.
I booked the basic room and NUA'd to the Adahan Charm Suite (Still called Signature suite in their system but it shows up as Adahan Charm Suite on their booking platforms). I arrived at the property at around 4pm and the suite was available.

Things I liked:

• Loved the overall aesthetics of the property and the hard product of the suite itself. High ceilings, great spacious foot print and layout, felt new and polished (for the most part... wooden floors did not withstand luggages too well) while maintaining the rustic charm of this old heritage building.
• Fantastic shower. It feels like I'm not doing the showers justice by calling it a rainfall shower head, it was more like a rainstorm shower head. Great temperatures and pressure and volume. Probably top 5 showers of all Marriott Bonvoy properties
• If you like having a cold room, this is the spot. AC runs quiet but blasts cold air consistently.
• Great a-la-carte Turkish Breakfast included for Plat+ in their rooftop restaurant (7am - 11am on weekdays, 7am - 11:30am on weekends). Cheese/Bread&Pastry/Fruits/Veggies/Cold Cuts/Flat Bread/Various condiments for bread come as a staple and you order beverage and other hot items to go with it. No limits from what I can tell. The offering was slightly dialled back from what I saw ElevatorEnthusiast receive during his stay but very minor (eg: less fruits and vegetables per order but can always request for more)
• Central location in Galata, to rest of core Istanbul. Aside from Balat and Kadikoy, everywhere was ~30 min walking distance so we walked everywhere. The hills weren't bad either. Surrounded by restaurants, bars, and cafes if you wanted to grab things near by (my recommendations are Antiochia and Asmali Mescit Durumcu which are 1 min walking distance. Highly recommend reservation for the former)

Things I disliked:

• The housekeeping staff here don't seem to have the eyes/touch for a level of detail you'd expect in an Autograph Collection property. They've forgotten to provide body lotion, half of the amenities provided in boxes were EMPTY, and the turn down service might as well not exist, as I'm not sure what they exactly do at this property.
• Chromecast does not seem to work (through tv.marriott.com). Tried connecting to living room TV but the code given connects to the bedroom TV. The two TVs seem to give out the same code. Can however connect direct to HDMI for whatever you need.
• Tap water is not officially drinkable so the property provides 2L of water a day, and any additional would incur additional cost. If you're staying solo this might be ok but as a couple that drink a lot of water daily, it's not enough. From previous experiences at properties where tap water is not drinkable the property usually provided additional water on request for free, so to see this not practiced here was somewhat bothersome. Though the workaround here is to go to a supermarket around the corner and buy a 5L water for 34.50 TRY (idk if is practice in Turkey to round up to nearest whole lira or I got played because I'm a tourist, she'll charge you 35 TRY), or just grab water bottles from the gym. The latter availability also made it a rather head scratching moment as to why they'd charge for additional water.
• Questionable TV placement in bedroom. It was rather useless.

Things I hated (yes, hated):

• I don't know if this a common thing happening on Friday nights and Saturday nights but the club/bar near by would be blasting awfully loud music from early evening until 3 am. And I'm not talking about just general loudness of Galata, I knew about it being a louder district. I'm talking outdoor EDM like loudness with each bass beat causing your chest to thump, piercing through the paper thin walls with ZERO sound dampening. If you stay on the west facing side of the building (ie: where all the Adahan Charm suites are located), you will be facing the full might of the music. You will NOT be having any decent sleep if you stay during Fridays and Saturdays. Heck maybe even Thursdays. Can confirm Sunday and Monday nights were peaceful. When I casually brought this up during a conversation with a guest relations staff, she just offered ear plugs but I don't think she realizes how loud it actually gets at night. Did Marriott Bonvoy even know of this when they added this property under their portfolio?
• On the window sills there are spot lights that shine bright light upwards during night. For whatever reason, the window next to the bath tub does not have blind or curtains, merely a frosted window. Accordingly your bedroom will be lit quite a bit during night and will not be possible to get an acceptable level of darkness for deep sleep. One hack I discovered was to take the box of bath scrub they provide, open the bath tub window, and cover the spotlight with the said box. It does not perfectly seal the light unless you have some sort of tape for the top opening. But even then because of street lights outside all you'll have achieved is just dampening the lights down a bit. Still impossible to get nice darkness level for sleep. Total oversight here.
• All in all, I had the worst quality of sleep at this property across all my travels in the past three years

Overall I cannot recommend this property to most folks. There's a lot of good things going for this property, especially the hard product you get for the price. However ultimately a hotel needs to absolutely nail one things and it is to offer guests a quality sleep at all times of the week which this property fails to do. I can only recommend this property to tourists that will not be staying Thursday to Saturday, or to party goers that will not be returning back to hotel until 3am or later. You can potentially mitigate the loudness by staying high as possible and as east as possible but that's still at the mercy of hotel upgrade choosing.

There are far too many great options in Istanbul for me to return here for the positives, to subject myself to poor quality sleep. I'll most likely be staying in Karakoy or Niksantasi next time in Istanbul. Galata and Fatih are far too chaotic for me to consider staying in as a returning traveller.

Pictures below: