I’ve never paddled the Fenn LS, but did buy a new Fenn Tarpon S, deep seat, adjustable footwell spec ski a couple years ago. Tarpon spec is foolproof rock solid, about like an XT. Tarpon is more stable than LS, though not sure by how much. High end competitive spec skis with very high seats/shallow buckets are very tippy. The deep seat version of LS will make it more stable than the ultra tippy specs. Compared to SE, which I consider elite level ocean ski, LS has to be more stable. May be more in line with your V10. Specs skis are totally different than ocean skis. Heavier/more durable, more rocker and front volume to surf steep nearshore breaking waves better. At 19’, specs are typically shorter than ocean skis. I had the SE and I think it was more like 22’! I would never consider taking a 22’ ocean ski where 19’ spec skis go. I use my SF S for offshore swell surfing and my spec ski for near shore surfing on breaking waves. Love them both, but for totally different purposes. I am not familiar with “river mouth.” If that means more like breakers/foamies or steep waves, I think spec would be good.
KR McGregor Rhythm, V10Sport, Swordfish S, Fenn Tarpon S, Fenn XT, Twogood Chalupski, Findeisen Stinger spec. Had: V12, Stellar SE, Huki S1-X, Burton wedge2, Fenn Tarpon