I would say don't waste your money. Kids at that age are still growing into their bladders. Your biggest mistake is using the pull-ups. It lulls them into a false security and they know that if they pee in it, there's no discomfort.
Get a good bed liner that is vinyl lined (walmart has them for less than $20, I think) and be prepared for a few nights to be woken (sp?) up to change the boy and the sheets (or just strip it down and wash first thing in the morning. This is really the best time for this as school is out, so losing sleep isn't a problem for the next day.
Make sure you don't scold him for wetting the bed, let him know its natural, but that he has to get used to the feeling that he's got to go and has to wake up to go to the bathroom. Also, limit his liquids at least an hour before bed-time and make sure he goes before hopping into bed.
I went through this with my younger daughter til she was seven or eight (it really only happened occasionally the older she got). But the key is them getting to not like the feeling of wet underwear AND not causing them anxiety. Let them know that their body is still learning, just like their minds are.
If it continues for more than a couple of weeks he may have a bladder issue and you should consider a doctor's visit, but I really doubt that will happen. Once he feels that wet, cold pee on his skin and sheets...he'll learn to wake up and go to the bathroom. Good luck and be patient!