I knew those blue folding taps as Scotchlock too. The trailer rental places used them and often not all that carefully.
Carefully applied, they'll serve "OK" for quite awhile. Easier things to do than have the wires positioned "just so" AND get the pliers "just so" and make the squeeze without something getting out of place or crooked. I've reconditioned a lot of those by squeezing the little metal insert so the notches are right again.
On a boat, in wet places, where they can't be stabilized from pulling or vibration, nope. But they have their place (well, a few place....).
Those Bell Tel connectors are pretty nifty. They include a gel inside to keep corrosion out of the pinched wires. Carefully engineered for a certain application to a certain type of wire in a certain environment applied by a trained tech with a certain tool. But I've seen them misused too.