Restorer are useful in lower level ships as they allow them to have decent SD at lower level for non-UK or non-MN BBs (that have a +2 national restore bonus to each sailors) without going overboard with the vets.

The main issue is that this restore will take a leveling spot on your ship, and its going to be especially costly if you are leveling with only one BO your crew, since you'll hit the BB6 with a restore around lvl 90 that you dumped once you hit 900 SD with the rest of your crew, and support lagging behind to be able to use it.

The true use of the restorer are on CVs, that use a restore and a repair on their R slot.

Since they only have 2 support, the CVs restorer never gets useless as they won't hit 900 SD unless going overboard with vets. And really massively overboard, with a seaman and a elite rep BO.

But as far as BB go, I'd say concentrate on your reps and engies.