I can't speak take for the Weber product but I strapped into and unstrapped from various versions of M-B seats a few times in my formative years and it's not a easy, quick, simple task to unhook yourself from a ejection seat and climb over the side, even in the event of a raid egress on the ground from an intact aircraft. It can also be fraught with risk if the seat is live.
I think you can use the manual separation to egress rapidly in a ditching situation. The parachute will come with you, but so will the seat pack. I'm sure that was the procedure on the MB Mk4 we used on the JP where you needed the seat pack for the dingy.
Although we were taught turnbacks on the Jet Provost when I was a student in 62/63 its one reason we later stopped Low level turnbacks in the RAF many, about 40 years, ago.
When I trained on the JP in the mid 80s, students were briefed to eject after an EFATO, only the QFIs were allowed to attempt a turnback and IIRC, the parameters were 160kts and 500ft. The Mk4 seat parameters for ejecting were 0/80 and min height in the descent at 1/10th of your decent rate. So descending at 2000fpm, you needed 200ft minimum.