They are coarse pitch at the root and fine pitch at the tips. It doesn't matter how they are supported. With wooden ones the mounting is the original board and it is natural to cut back the trailing edge so that the TE drops behind the mounting point.

For curved sheet blades you can mount either way. TLG use the method shown and it probably has some advantages in terms of strength and clearance.

It is probably necessary with pvc to use these large coarse pitched sections at the root to get sufficient strength. They probably suit low speed operation where large starting torques are required such as "draggy" dc motors.

I am sure that if you keep them to low tsr ( below 5 or perhaps better below 4) they will work fine. The result is that you need a slower larger and considerably more costly alternator for the same power out. I don't think they are interchangeable with the Dan type projects intended for wooden blades.

I have not had any real experience with them, the only blades I ever tried to make from pvc were more trouble than dealing with wood which I find easy.

I have recently had a chance to compare an early Freelite prop made from sheet aluminium alloy with the later wooden one. This is a fast prop by modern standards and the aluminium ones has significant less pitch than the replacement wooden one at the tips and is tapered and twisted. The wooden one has little taper and no twist. On the Freelite the wooden one is way better faster and quieter than the aluminium one and I suspect that the aluminium one would need a slower and larger dynamo for equal results.

I think the curved sheet things behave far more liked cambered aerofoils. We tend to think of the pitch in relation to the front surface of the wooden ones and that is reasonably justified with the Clark Y type profile that they approximate to.

The pitch should be related to the line joining leading edge to trailing edge and with the cambered sections the lift will always be higher for the same pitch angle. For high speed the pitch of the single surface things ( pvc etc) will probably have to be negative to be equivalent to the wooden types. If you do this I am sure you can get the speed up ( Suspect drag will be a lot higher). The snag is that you will not have enough strength at the centre to support a high tsr type.

For normal operation except for the dc motors and possibly some conversions with bad iron loss and cogging I am convinced that this large chord and pitch at the centre predicted by calculators is not beneficial and is probably detrimental with the constant speed loading  as approximated to by battery chargers.

Even with mppt loading I still am not convinced about this large coarse pitch middle section, in fact I am not convinced that the middle third of the prop is other than a hindrance and I suspect the wind flow through it is not as predicted.

Anyway this is mostly speculation based on my own findings, everyone to their own choice, I couldn't be bothered with pcv but as I have been carving wooden ones since I was 10 I find it easy and can't see any point in doing otherwise.