Flytyer, look in the archives for info on trim tabs. There has been topics about Bennett trim tabs. Saying that, I will give mho again about trim tabs. My 18.5' Double eagle 75 vintage came with trim tabs, I'm assuming they are original with the boat.One minor repair for me, so top marks from me for reliability. This is the first boat I've had with trim tabs and after experiencing what they can do for ride control I can say now that any boat I own in the future will ABSOULUTELY have to have trim tabs.
In answer to your questions, I would say they will work fine on your 19' boat. Cost I don't know. Auto level feature I don't know, but it sounds like a gimmick to me.
Bennett's website explains the whole theory on how they work quite well. It's basic hydraulics. You get port and stbd control plus fore and aft control. Trimming a leg i/o or outboard only gives you fore and aft but the problem with that is it takes away from the efficiency of the propellor
Highly recomend them.
And no I don't work for Bennett.