Personally, I wouldn't bother with anything other than the plastic blocks if you're running on rubber tyres.
The alloy ones give you some adjustment for sure, but for robber tyres, the std plastic blocks are fine - and a fair chunk lighter than the alloy ones.
I'm not sure I saw any of the UK team run alloy blocks last year.
I haven't had a set of alloy ones on my car since the day I got plastic ones for my pre prod car.