Mallet/spanner/buff has become popular for engineers who don't really need to fight much fire (which has become more common since the fire nerf) and who gain more from the extra repair ability. This goes for the top right engi on the Pyra, one of the Squid engineers, one or two Junker engineers, the Goldfish buffgineer, and that's about it.
Also, I'm changing my mind about the meta next patch. Greased rounds are terrible. Still engineer x3 for the Pyra.