mucky We are totally loving the beds - would definitely recommend! It was a big decision for us and we, like you, were tempted to just get a bed from JL/IKEA; but with multiples we rarely splurge on big things because you have to buy 3 of them, whereas if we only had DD1 and DD2, then we wouldn't think twice about it, IYSWIM? Its a bit hard to explain, but if I had 5 singletons then I would just buy the beds (rather than having to bulk buy!) so I don't see why DTrips shouldn't have them! 
I have to say that I think it would be really hard putting your DT's down for a nap in the daytime, in beds. At night time they are totally shattered, its dark and they've had 'wind down' time - in the daytime I think it would just turn into one huge game - so I don't blame you for keeping them in cots whilst they're still napping. Then again, if you are currently cutting down on naps, they may be even more tired at bedtime and therefore more likely to stay in their beds rather then get out - out of sheer tiredness!
Dtrips were still potty training (still are!) when they went into beds and, personally, I don't think it was too much for them - but I can see why you think it might. We did find that if they were naughty going to bed, and so went to bed really late, we would have lots of accidents the following day because of tiredness.
We still haven't cut out dummies yet
Actually feeling quite guilty about it now. DTrips were 3 in June. Bedtimes are still not good, and by cutting out the dummies I know that they will just be a total nightmare. When we cut out DD2's, that was when the bedtime problems started, because she didn't have anything to help her fall asleep. A dummy gives them something to concentrate on, but without it I know DTrips will be awful. It will then have a serious knock-on effect on behaviour (still being v.naughty with all this 'no' business - no threats put them off - more on that later..) and then knock on effect on potty training too because they will be up til some ridiculous hour. I think they will just be big babies' forever!
But yes, the behaviour is not improving and I really am at the end of my tether. We've had the same with DD2, but I can easily pick up one kicking, screaming child and put them in time-out, but it is virtually impossible with 3. I'm beginning to avoid taking them to public places like the supermarket because of it, which is absolutely ridiculous - you know you've got a problem when you can't even take your own children to the supermarket.
DH took DD1 and DD2 somewhere on Sunday and I only needed to get a few bits from Sainsburys (wouldn't do a weekly shop). Firstly they flatly refused to get shoes on - i.e, I would stuff their feet in and then by the time I had stuffed another childs foot in their shoes, #1 had taken theirs off. Once we were finally in the car and at Sainsburys, they wouldn't get out of the car - in the end I just had to go and get a trolley, grab them out the car and put them in the trolley. Once again, once I had put 1 in and gone to get the other, #1 had climbed out. I had tried all bribary and threats and they just carried on saying 'no' and laughing. I'm too stubborn for my own good, and wasn't going to go home now! They then started behaving slightly so I agreed that they could take turns in walking (2 in trolley, 1 walking). 'A' was walking and then sat on the floor and refused to move, kicking me at the same time. I couldn't stuff her in the trolley as we'd put food in it by now (a few more bits than I'd planned). I picked her up and stood her on her feet, but she just laughed and collapsed back onto the floor - welcome back 'jelly legs'. After 10 minutes of reasoning and bribary, and her being incredibly rude, I picked her up and stuffed her under my arm and carried on shopping. She started kicking off and somehow managed to get down (even DD2 couldn't do this!). I had had enough and was a total evil mummy and said 'If you don't start being a good girl and behaving, I will take you back out to the car and leave you there whilst I do the shopping'. (No matter the behaviour, I would never do this, but I genuinely thought she might snap out of it) She was still smiling and just kept saying 'No!' as though she wasn't even bothered. What happened to my lovely girls who rarely said 'no' to me?! Other 2 girls were laughing at her and basically egging her on so I abandoned shopping, mid aisle, and frog marched all 3 back to car where I stuffed and strapped them in, locked the car and then stood by the boot of the car where they couldn't see me. Just stood for a few minutes and calmed down, then got back in car and drove, silently, home.
I still cannot believe that I had to abandon shopping - even with 3 stropping 2YO's, or screaming babies, I've not given in and gone home! But with 3 year olds?!?
Worst part was, when we got home and DH came out to get them in and could see how angry I was, he said that he thought they should apologise to me for their behaviour; all 3 went like this:
'Showwy!' and went running off happily into the house!
Literally, within seconds they go back to their normal, lovely selves - but when they are in the 'no' zone, they are awful.
Sorry for whole running commentary of our Sainsburys trip, just needed to vent!