H imate. I had a Kappa box some years ago which is a sub-brand of Givi and was very happy with it. The mounting was a little hard work - my first ever bike mod so inexperience slowed me down - but in everyday use it was the mutt’s.
Just go for a good brand, one that stands a good chance of supplying a mount for a new bike in the future.
100% waterproof seems unnecessary if you always put stuff in a bin bag, and stability (on my Fazer) was un-affected.