I don't think it's a waste of time. I enjoy getting out and spending the day slow trolling along the beaches. I almost always have a good day of catching stripers when trolling. I don't use umbrella rigs that often though. If bluefish are around they will pile on and tear up the shads that I use. That can get expensive. I'll put them on only if I've tried everything else and I know no bluefish are around. My favorite trolling method is with large bunker spoons on wire line. I'll also troll large plastic lures alot too.
I love 'em. Can't stop laughing everytime one of the crew has to crank it in. They'll jump on the rod everytime, but run out of steam half way in. Obviously, I drive the boat. Tubes in colder water, shads in warmer.
Use them in Raritan bay work great. Troll at 3.5 knots. Most people use wire line. Rule of thumb is for every 10ft out goes down 1 ft. In 20 ft of water 200 ft of wire. Want to keep them near the bottom when depth changes have to work the lines.