I have been on flats a while now.
The new large platform pedals are great.
Myself I like the metal pins, your feet stick to them.
I have a pair of Shimano Saints which are kinda concave and are great, I have been using them for years and never pulled them apart although I was going to and seen how small the bearings were and just pushed some grease in them.
I also use Crank Bros Stomp. I like them but the axle is a little higher in the middle and sometimes bothers me.
I used two pair of cheap flats off of Amazon, Foker, and they held up well but wouldn't trust them for aggressive mountain biking. I left a pair on my daughters bike.
My first knee replacement is next week and I shedded the clipless two years ago and probably will not go back.
Also it is nice to get off the bike and walk normally. I use athletic shoes, hiking shoes and leather boots in the winter.