Don't expect a bargain when it comes to a *GOOD* BHB. And you need to be careful even with pricey ones.
Check the bristles for adhesive contamination; the adhesive should *NOT* extend out of the block up into the bristles or it'll cause issues in time.
CD-test after soaking the BHB in water/detergent mix for a while (don't test it dry).
The softest BHBs might be too soft for cleaning truly soiled surfaces; the not-so-soft ones might be soft enough to be safe, but they might *not* be. You simply have to test each one and keep testing because they do eventually wear out (the flagging wears off the tips of the bristles). I have "too-soft" ones that I use on the good cars and not-as-soft ones that I use on the drivers; neither causes marring in-and-of itself.
A *good* BHB will last for a long time though. But note that the smaller ones I'm always hyping seem to wear a lot faster than the bigger ones. Might be because the little ones get used differently :nixweiss
But IMO you're not paying for durability; you're paying for the unique features that a BHB brings to the table. Those features (free-rinsing, the ability to be used in a *VERY* gentle manner with the *right* technique) are gonna be lost on people who don't use the BHB properly.
If you just scrub the paint with it it'll be a scratch-machine no matter how good it is. If you use it without a foamgun, well....good luck with that. If you wash a whole panel without rinsing/redunking in shampoo mix, well...good luck with that too. Used to make the job go quicker, I predict a lot of wash-induced marring. Used to make the job go *smarter*, I predict a big *drop* in wash-induced marring, but it'll be more work too and you won't get the technique right the first few times.
Note that when a BHB is used properly, you'll have to follow up with some more aggressive wash media to get the more tenacious road grime/film off. It's just too gentle to be used all by itself. It's best used to "knock the big stuff off" safely, much as others use a pressure washer for the initial pre-wash (a viable alternative IMO).