I have the Silhouette XV large glider which I am using instead of an older Silhouette Sphere 2 29" spinner. The idea of the "gliders" is that they are positioned horizontally instead of vertically. The large glider is quite large but a bit smaller than the 29" spinner. It's wider but shorter than the 29" and total cubic inches are less. I would think you are considering the medium glider which would compare the to 25" vertical spinner. It would be easy to compare the dimensions of each but I would assume its a tad smaller than the 25" just as the large glider is smaller than the 29".
The Silhouette XV line is not new and I think Samsonite is in the process of discontinuing it. I bought mine on Amazon about 2 years ago, it's showing as currently unavailable on Amazon now. You might be able to find clearance inventory on this item somewhere. I paid about $200.
After 2 years and 10 month long trips to China, my XV glider is nearly new, no lost zipper pulls or broken wheels. I've had no operational issues with the handle. The locking mechanism seems a little cheap, still working on mine without issue, but seems like a part that could fail. One benefit of the horizontal design is that its good for stacking a carry-on on top. However, true for all on the XV line, the handle is quite wide and I've yet to find a backpack or bag with builtin band to be wide enough to slide onto the handle. I end up using a travel bungee if I want to stack. I'm not that happy with the exterior pockets, there's a smaller on top and a larger one below it. They both don't open very wide. The larger one could accommodate a light jacket, umbrella or maybe some paperwork. The small pocket is very short, I keep a luggage bungee in there.
I tend to pack heavy and bring gifts and other items with me, so my large glider can get very full and heavy. I've not gone over 70 lbs, but I've come close. When very heavy, the horizontal design keeps a lower center of gravity. Pushing on carpeted surfaces when fully loaded can take some extra work. That's my experience with the large glider at about 65 lbs. With being heavily loaded on my departures, I've not seen any damage to the bag when retrieved, so seems pretty durable. Being horizontal vs vertical, drivers and bellman get confused always trying to put it upright. The design hearkens back to the old style of suitcases with out wheels, I'm not sure if its better or worse but it's been working for me.
The interior is fine, nothing special, with a bit of interior space lost due to the handle assembly. Hanging on the interior right side, is a thick seal-able plastic bag for liquids. Attached to the top lid are two zippered pockets, one clear plastic and the other nylon both about the same size. They are attached to a zippered pocket that I use to hold folded garments, dress shirts and pants. The bag came with a large folding hanger for this but instead I use a zippered tri-fold nylon garment bag that came with my Sphere 2 29". I can tri-fold about 4 shirts, 2 pants and put into that top compartment. The bag is deeper than vertical bags of similar size. There is a single retaining mesh that clips together from both side, top and bottom, positioned about 2/3 up. So if you use cubes to pack, can retain the cubes on the bottom while having looser items packed on top that will generally fall when the bag is moved from packing position to upright floor position.
I like the styling of the Silhouette line, looks smart and professional, they aren't cheap but certainly don't come close in price to the premiums brands. I paid around $200 for each piece, Sphere 2 rolling garment bag, 29" slider and the XV large glider. The nylon weave of the external fabric seems very durable and mines been very stain resistant. Samsonite touts the wheel design on the Silhouette line and it is quite different. Having had 2 Silhouette Sphere 2 pieces and this XV piece, I've never lost a wheel. Even though I have all black, it's easy for me to spot my bag from others because the wheel design is different than other bags. The XV glider is very easy to spot, since nothing else matches the dimensions along with the wheels.
I just wish the handle on the XV was a bit narrower to slide on my backpack. The Sphere 2 could accommodate it, but the XV handle is too wide. With all that said, I like the bag. I don't think they sold very well and could be hard to find now at a discounted price.