I have trouble gauging when Redeemer is a good choice. Here's the thing, the 4 extra attack for your opponent from the gauss charges mean that you will have to buy extra defense one turn earlier. That defense is not only expensive, which means building up little or no pressure on the turn you build the defense, but it's also a huge warning sign for your opponent, who can react accordingly (eg., profit from the temporary reprieve to build up a lot of pressure, and deny your redeemer build, putting you severely behind).
If you build engineers to counter the gauss charges, the total cost of your Redeemer is 16GGB. It doesn't compare very favourably to the other 3 attack units in the game (Asteri cannon, Drake, Omega Splitter, Cynestra)
So, redeemer seems sort of a tough sell without good support (mainly Chieftains and Antima Comet, I think, or as a counter to periodic attackers). Anyone else with a differing opinion?