I've been reading a few posts here about which focusing loupe to buy and I got confused.

I learned that horseman, toyo and wista are some of the best focusing aids around, but I also found some people saying that regular negative loupes work good as a focusing aid. Is that so? I had the impression that a focusing loupe had an offset for the focus point in order to account for the glass thickness.

I know you get what you pay for, but I guess my question is if using a cheap (around $20 bucks) loupe is better than no loupe at all?