We went with the Disk-O-Beds last year. I originally purchased one set then quickly decided that my kids would no way let mom and dad sleep in them so waited for REI sale and got another. To sleep on, they are awesome. We put a thermorest on and you are good to go. Saves a TON of room in the tent for walking around and getting out of the tent. A couple of draw backs are they are heavy, take up a considerable amount of room when transporting, especially 2 sets, and not a quick set up and take down. Oh and expensive. Once you are past that, they are excellent. I would say the pros outweigh the cons if you have a family of 4. If it was just the wife and I, I'd go with regular old cots and save a pile of money.
Have you seen the Kid-O-Bunks? They are just like the Discobeds but a bit smaller for the kids. I've got a set on order but that's our plan for our ground tent and to put the kids on in the RTT's annex when I get one. I like my disco beds, & my dad got the Arm-O-Bunks off eBay for cheaper than the Disc-O-Bed, they're heavier duty and made in the USA.
The discobed is not as comfortable as the RTT, but I think it's much better than an air mattress. I do need to try a cot pad or Thermarest though, that may make them more comfy.