Sorry but the water line blue and white flowery tiles look old fashioned and if you're going for that kind of sandstone on the top it won't go with the terracotta tiles you have already Do like the pool and tiles that Hayda Natural Stone have posted Very nice!

We used concrete look tiles in our bathrooms, and decided on the same tile (outdoor version) for our pool area. We also used it for our pool coping and waterline tile and edge of the steps. The tiler cut the tiles, and we had a guy come onsite to hone the edges (same effect as the ones in your photo, but same tile on coping and waterline) who did a wonderful job and really reasonable price. This may not be what you are after, but we did not want any glitzy tiles. Photos below

Potentially yes if they're cut/laid badly - I was involved on a job that $30K(ouch!!) of glass mosaic's were jackhammered out and completely replaced because the overall finish was deemed that poor and dangerous - the entry steps were too risky to use and there were tiles falling off before it was filled!.......That was a particularly bad/unfortunate case, and not wanting to completely scare you off the idea, if the the pool design has limited/deleted any underwater sharp corners or edges, and the glass tile install/prep is performed properly, then there's arguably low injury risk, and they can be a great finish if done correctly :)

it's never perfect and always involves a balance/compromise to achieve the less noticeable outcome - it's the decision with the convergence lines as to whether the base run is cut or the wall. That the wall run is cut it accentuates the pool fall more - if it was the other way around, in that the wall run comes down to a straight/horizontal line and the base is cut into that line the angle would not be as noticeable......you can fix it, and in this case arguably due to the window perspective looking straight on it's a justified request - adding water won't improve/soften the end result dramatically in this case IMO....that main thing is that it's been prep'd straight which it looks like it has been - this is only cosmetic remedial, which whilst yes will cost the contractor, you have to live with the end result so it's worth the (hard) conversation......good luck!