The main thing I have against suspension stems is that they don’t absorb hits or shocks to the bike. They protect your hands and upper body from hits and shocks, but do nothing at all to absorb those felt by the bike. I occasionally ride over very rough surfaces, enough that things which aren’t secured tightly to my bike, or even in my jersey pockets, can fall off. I’ve had to go back and look for my phone twice when it bounced out of my jersey pocket (I now keep it mounted to the stem with a Rec Mount). I find comfort over the rougher places I ride to be more important than all-out speed.