Regarding the cost, some BHBs wear like iron. I still use one I bought in the 1980s! You need to keep an eye on the tips of the bristles (the split ends, AKA "flagged tips", wear down) but that takes a while and they don't instantly turn into scratch machines the way synthetic bristles do when that happens. Same old story- CD-test your wash/dry media both before use and at regular intervals.
Regarding how well they work, I'd advise to beware of marketing hype, even when it's about stuff that I like
If you "scrub" with them you'll mess up your paint same as with a mitt. The best features of the BHBs (and the primary reasons why I recommend them) are:
-Free rinsing nature: Used with a foamgun the dirt gets flushed away so it doesn't have a chance to mar the paint. The basic idea is "dislodge and flush" as opposed to "scrub".
-Ease on controlling pressure on the paint: With a little practice, you can easily use the BHB more gently than a mitt, you just *barely* touch the paint, not enough to really bend the bristles. Only the tips of the bristles touch the paint (where they dislodge the dirt). That's harder to do with a mitt and more pressure = greater chance of marring.
It's not like I don't like/use mitts; I use them for a light follow-up after using the BHB to get the worst stuff off, which I consider to be the most likely to mar the paint. If there's something *really* worrisome on there, I use a siphon-feed sprayer that hooks up to my airhose (sorta a low-power pressure washer) to get it off before using the BHB/foamgun.
Note that no wash media oughta disturb the wax/sealant. The *shampoo* might compromise it, but not the mitt/BHB/whatever. You *never* want that degree of scrubbing action going on IMO. If something doesn't come off with very gentle wash techniques I use Sonus green Ultra-Fine clay to remove it (and I do that *very* carefully).