My favorite base coat so far, especially as it really does seem to make manicures last longer and prevent nail color from staining the nail... and the colors I favor are bright reds, vampy reds, and dark-almost-blacks, so this is saying something. I used to get really bad stains in my nails whenever I wore nail color, but this seems to keep it almost entirely at bay.
However, the orange staining from the base coat itself, that other people here have mentioned, is definitely there. I’m lucky, though, in that that isn't a problem for me: my nails have a perpetual blue tint in the nail bed that almost looks like cyanosis (but it's not, they're like that even directly after an intense workout) and this actually corrects for some of that, especially if I use a light sheer "My Nails But Better" kind of polish over them.
As for weakening the nails, I guess I haven't used this long enough to be a good judge of that. I will say, however, that after using this base coat for about a month, I'm actually able to have long-ish nails for the first time in my life... and the nails are even LESS prone to chipping and splitting and flaking than they used to be. This is the case even though I do a fair bit of cooking and cleaning and washing up at home, and often dispense with gloves out of laziness. I guess that might just be because I've been more aware of my nails since I've started giving myself regular manicures, and started using my hands in a way as to stress the nails less. I've also been applying cuticle oil regularly, which I didn't really do before.
But I also think having to remove my polish less (because the manicure isn't getting destroyed on a regular basis, just wearing down a bit so touch-ups are all that's needed) and therefore having to handle acetone less frequently is also helping the strength of my nails a lot. I can go longer without having to expose my nails to the harsh chemicals, and that’s partly thanks to this base coat. I've noticed especially with Bonder that there isn't even a need to "strip" the nails with alcohol or acetone before applying the polish. I simply wipe off any residual oils with a cotton towel or a buffing cloth, and I believe this is also what helps my nails stay strong and flexible and flake-free from the inside out.