This apartment was awesome. The photos don't do it justice when you take into consideration the amount of space and the location. We had 4 adults and one baby and we all felt like we had plenty of space to relax and not feel like we were in each other's way. As for location, the apartment is right on Corso Cavour and is a short walk (uphill) from the funicular. The apartment is also super convenient to lots of great restaurants, shops, and sites (like the Duomo) which was great considering that we had a baby that needed to nap and eat on a regular schedule. So popping in and out isn't at all out of the way.
Tomas met us outside of the apartment and made sure we were all set before leaving the keys. Both he and Anna Maria were super quick in replying to my messages and texts (SMS).
Other things I thought were great: plenty of hot water, good water pressure, comfortable beds, plenty of towels, very spacious rooms, fast wifi, and a nice kitchen. I'm probably forgetting things but that's what I would want to know.
Note that since the apartment is on Corso Cavour there will be street noise that you hear from two (of the three) bedrooms. It didn't bother us as we live in an urban setting ourselves. This is, of course, no fault of the hosts.
When we visit Orvieto again -- because we will be back -- we will definitely check to see if this apartment is available.