The f2 is a solid choice, decent range of programmability although if you've got a low fps limit you'll need to invest in a low flow poppet to help it run better, and unlike the fusion you can swap it over to an ak if the fancy takes you.
Mine's been solid for over a year now with basically no maintenance and zero issues but as druid says your milage may vary depending on how you treat it, although i've never heard of a polarstar failing that wasnt due to some serious abuse.
Of course working and working well are 2 different things, hpa is no magic bullet and whilst they can certainly perform well when set up right, but equally they can be terrible when set up wrong, and there can be a lot of tinkering and tuning to get them going well.