I too usually end up soaking off Bio enhancements every few infills....some clients look after their nails well they can go for several sets, but some need soaking off every couple of visits.
Calgel, for the small amount I've used it, files down better, but a lot of the reason my clients prefer to soak off is I have a lot that use colour and they often want a colour change. Although with Bio you are trained to put a layer of clear under the colour, so thyeoretically you could buff down to this, whereas with Calgel, I believe you are trained to put colour straight on the natural nail (please correct me if I'm wrong - I'm not Calgel trained, that was just from a conversation with their rep at an exihibition)
It does seem to be that Bio as it has a slightly more rubbery and rip-able (is that a word?) nature than other soak-offs (albeit the spongefiles are great with Bio and if you use them it does't rip at all), but in all honesty it soaks off so nice and quick that the nails are not only unaffected, but most are actually in lovely condition..
To be honest I'm such a lazy devil that i never buff my own down and pretty much always soak off - and I get bored quickly, so my nails are usually removed every couple of weeks and honestly they've never been in better condition.
i think it does require clients do ensure the do their aftercare for real tip top condition, but then all systems do.