Some comparison with Rakza Z / Rakza Z Extra Hard, please?
Hi, for me these are very different, the DFVP (and rubbers like H3, B2, etc.) have this dense micro-porous sponge, they are sometimes called linear, or dead, or whatnot. They simply have their characteristic feedback... ;-) The Rakza Z has at least a bit porous sponge, it is also not very fast, slightly tacky, but still has (for me) the ESN heritage.
The RZ is H37-H38, I measured it, it is less than declared, about the same as Rakza X (which nominally is softer). It is not a bad rubber at all, just not for me. I much prefer RX on the BH, and on the FH I prefer harder, like H40/H41 and micro-porous.
However, I did consider trying a bit more porous sponge with that hardness on the FH, so I tried BlueGrip C1/C2 and J&H Z52,5, and I also considered RZ EH, but I didn't try it yet. I think it could be quite good, but now I have couple of other sheets to use, so can't serve here, now and in the foreseable future...
The DFVP - I still have 2 unused new sheets in H40, if you happen to come to the czech TT-forum meeting, I offer for 80% ;-). However, my impression is that the durability is not very good, but given the price, it's OK.