I wouldn't worry about it strength-wise as long as the enhancement is properly structured, the tip offers no strength at just a platform to build on.. What I would worry about is water getting trapped underneath and the client coming back with a lovely green bacterial infection... It's the same as lifting you just can't apply new product on top without removing it first, it will be a breeding ground for bacteria.. On a rare occasion I use tips and an even rarer occasion I get an air bubble it always goes away once I've properly blended the tip flush to the natural nail.