I like the idea of the sandwich adapter better than the in-line thermostat just because it eliminates the extra fittings and can be easily removed should a leak or pop-off occur. One less fitting is one less potential problem.
Doesn't help with the lines to the engine, but in a pinch you can also use one of the cooler lines as a quick fix.
Except for the track or some really hot days the cooler is of no benefit anyway. Nearly all engine wear occurs at lower temps and is almost non-existant once the
oil heats up and flows.