For sure you don't get something for nothing
Something like a SW Esprit 120 (
here) is "only" 2x the price of the MN190 and head-to-head I'd be _very_ surprised if the MN could put clean dark pixels between stars where the 120 couldn't.
Speed...yeah you got me
but it's a little less than an f/stop...
As for focal length, careful choice of pixel sizes and sensitivities should be able to claw that back under most sky conditions, shy of excellent nights. But when was the last time you had one of those?
