I know this has been covered lots and lots of times and I'm sorry but I really can't be bothered to read them all

I think if Iv got it right this is the best place to get one Www.obdtool.co.uk but witch one?
what do I need I run it an old laptop a tablet ? A net book? and can I really get it very wrong when using it on a van?? Is it like the snap on stuff that is basically yes no etc etc??
Sorry it's a lot but don't want to waste my money on junk that will just annoy me
Any help would be greatly appreciated