As far as if plastic pedals are good for grinding the answer is yes. i personally ride with metals primos but when i go to the skate park i switch out the left pedal for a plastic one. you slide a lot easier.
If you get a good pair of plastic pedals then they will be great for both trials and street but if you live in an area where there is a lot of rain then be careful.
ive seen guys ride street with plastic pedals and it worked good for grinding and they seemed to have good grip, as for me id never ride street with plastic pedals because of drops…
i use the butterflys for riding and ive pretty much taken out most of the pins on one side for grinding…they work good for me!!
jim c’s, primos, LX’s (plastic).
if you are grinding probably don’t go with the primos but other than that they are good
and sealed bearings means that the bearings are sealed to keep dust and water out.
from what I hear the type of riding most unicyclers do is enough to destroy the bearings fairly quickly.