I was going to get one of these for DS. We're going to Spain in September to a work-mate's appartment. DS will be 3 and seeing as there's another couple going, we'll need something for DS to sleep on in our room. It'll only be for a week and I thought it wouldn't take up to much of the baggage allowance.
They are handing things but,my dd1 who is 6 had one & one of the lines that go down in the inner bed burst open so she was up one end & down the other but i think it was because she was sleeping on it alot.They are ideal for holidays & as your son is only 3 it should be fine.My dd tells me they are comfortable.
I should think that they would be too hot for spain in September, they have a fleecy sleeping bag which you can't really remove. Ds is three and he always falls off his 10 mins after he goes to sleep. It is more of a toy than a bed IMO.