I've only stayed at an Execustay twice. Once was in Tokyo (Ginza) for 68 days and the other in Delray Beach, FL for 74 days. While my experience may not be the same as one in the Phoenix area, here's a few notes:

• Execustays are furnished apartments. Both of mine were in an actual apartment complex (which I presume most are). I was staying where local residents lived full-time. So, without mention, all the pros and cons of apartment living apply. For example, on two separate occasions, the water was turned off to the building for repairs. You won't be reimbursed or receive any type of benefits for this.
  
• You may be held to property rules, which can widely vary. At the Delray Beach complex, I had to adhere to the rule of all guests must be registered with the property manager a minimum of 1 business day prior to their arrival.
  
• You are responsible for the upkeep, cleanliness and general "housekeeping" duties during your stay.
  
• Rental fees, surcharges, etc. can quickly add up. My stay would've been several thousands cheaper in local hotels, but wouldn't of had the same amenities.
  
• If MR points and nights are important to you, don't plan on earning much with Execustay. It's 2.5 points for every dollar and 1 elite night is based upon every 3 nights stayed.

Long story short, I rarely recommend the Execustays. If I was in your situation, I'd rather stay at a RI, have housekeeping take care of the chores and enjoy some manager dinners/cocktail hours during the week.