Linear vs Circular Polarization. Which is better for the osmo pocket? I've read that Linear isn't compatible with some auto focus systems. But PGYTech offers the linear ND/PL for the pocket.

Linear isn't compatible with some SLR focus/exposure systems as they use mirrors to syphon off some of the light (via polarisation) and that splitting of the light can take the light from the angle that has been polarised and hence cross-polarised, which reduced/removed to a point where it can't focus or get the exposure right. It can be like stacking one polariser on top of another. Another way to see this is take an iPhone and turn your CPL around it. One angle you'll see the screen is black or almost black. This is because the iPhone screen itself has a polariser and if your CPL then is at 90 degrees to it, you'll get cross polarisation and no light. The linear PL and AF/AE beam splitting in SLRs can do the same and hence the AE/AF systems don't get any light to reference.
I'm not 100% certain, but I don't think this is a problem with 'live view' systems that take these readings straight off the sensor, which I assume is what the OP does (like a mini mirrorless camera).

On the Pgytech site, I can't see it mentioning that the ND/PL is specifically a linear PL, just it doesn't call it a CPL, but thats not to mean its not a CPL. I'm sure you'll have no issues with Pgytech anyway and they wouldn't release a filter that wont work with the AF/AE systems on the OP.  

Cameleon Posted at 1-17 00:57
Linear isn't compatible with some SLR focus/exposure systems as they use mirrors to syphon off some of the light (via polarisation) and that splitting of the light can take the light from the angle that has been polarised and hence cross-polarised, which reduced/removed to a point where it can't focus or get the exposure right. It can be like stacking one polariser on top of another. Another way to see this is take an iPhone and turn your CPL around it. One angle you'll see the screen is black or almost black. This is because the iPhone screen itself has a polariser and if your CPL then is at 90 degrees to it, you'll get cross polarisation and no light. The linear PL and AF/AE beam splitting in SLRs can do the same and hence the AE/AF systems don't get any light to reference.
I'm not 100% certain, but I don't think this is a problem with 'live view' systems that take these readings straight off the sensor, which I assume is what the OP does (like a mini mirrorless camera).

Thank You for the reply, That's good knowledge to have. Now which would you prefer for the pocket? Circular or Linear? I get the feeling most would prefer circular, but linear seems more fool proof.

Circular or linear makes no difference assuming the linear PL is compatible with the sensor of the camera (which I think is true with the OP).

I think what you may be asking is what do I prefer over a fixed PL or rotatable PL. The Freewell filters are rotatable (via the ring) to allow you to set the angle of the polariser to allow you to get the maximum effect from the polariser, whereas some are fixed. If you are asking which I prefer out of them, I've not used them enough on the OP or my Mavic Air to decide for video. For stills photos, I prefer to have the rotatable one to pick the amount of polarisation I desire. In video, I think its just a nice benefit to be able to adjust it but its not a deal breaker, as by the nature of video, you tend to be moving and the polarising effect varys and its not really feasible to try and adjust it mid shot!

So I would just go with the filters that best suit your budget as to be honest all the ones mentioned on here are great and it's not like we're shooting for a Hollywood movie! PolarPro, Freewell or Pgytech will all be fine.