some guys are using them on four strokes, however the ones I have seen are pretty bulky and appear to need lots of work. IMHO

These are for electric?
At least for my Super Clown, I tended to go high pitch, because I think electric motors really are different that IC mainly because their torque rises as rpm drops. Of course to keep efficiency up, the motors which can use high pitch props will be the ones with a relatively low kV --or a higher kV used with a lower cell count battery (rpm=kV * battery voltage).
The main question is how the entire system behaves when you turn the nose up---will the pulling power be there --it should, but nothing works like real data.
For  the Super Clown I ended up with a 10-7 APC electric which worked quite well. I have a 11-5.5 APC electric on my Nobler, but the Jury is still out. One problem with high pitch, you still need blade area to make up for the lower rpm to make thrust, and you are limited by the diameter that the plane landing gear can support--to prevent blade strikes. I would love to see 3 and four blade APC props like their 2 blade electrics--nice and thin,

So getting back to main question (sorry for the long diversion), if these are electric props, it would be dangerous to use them with glow engines. The power puls delivered by the one power pulse per revolution (or every other revolution for a 4 stroke or a 4 stroking 2 stroke) gives quite a shock to the prop, An electric is much smoother since it is giving power basically every time a magnet moves over a pole piece, so 10 or more times per revolution. As Paul mentions, the root of the prop is pretty thin on electric props.