Bug-wise yes, both Photo and Designer are very very buggy.

Functionality, also yes, but not by much. Only thing I miss from Photoshop in Affinity Photo is content aware tooling. I don't remember anything I miss from Illustrator in Affinity Design and I actually think they have better features than Illustrator (admittedly haven't used Illustrator in almost a decade so maybe they've caught up).

You really can't beat Affinity's price though unless you use GIMP/Inkscape of course, but I like neither of those programs.

To chip in to on this, I've been using Affinity Photo for at least 5 years and I don't remember having many problems at all. That is to say, YMMV.

Yeah photo is leagues less buggy than designer. That said, I've had random crashes with Photo in the past too.