Edward, the purpose of the TC saver is not to prevent wear to the TC. There are several situations while towing that the advantage of unlocking the TC becomes evident. Like cresting a big hill with a heavy load, and the last couple of hundred yards, you don't want to slow up to catch the next lower gear, so with the TC saver, and the DTT converter, you can unlock the TC, raise the RPM's 200-300, and finish off the hill, let off the throttle and back to lockup you go. This is a true benefit while towing heavy.
As to why 3 out of 4 use billet covers, maybe they need them, maybe they don't. I know that the DTT converters I install do not, as they don't balloon, or fail, period. That sales pitch , is just that, a sales pitch.