The PWK appears to be a nicely made carb at a quite amazing price, plus a wide range of pilot & main jets are available. There have been a couple of articles in MZ Rider recently WRT fitting these to MZ 250s, with jetting recommendations & apparently they work well.
Unfortunately both the mounting and air inlet stubs are smaller than the OE BVFs & the overall length is shorter, so a re-engineered mounting & airbox connection is required to make one fit - it becomes a "project" rather than "simple replacement". Plus the throttle cable needs to be modified & they are a knob operated starter jet rather than cable operated (not that that is a major problem).
There is another Chinese carb available, which appears to be based on the Mikuni VM round slide carb rather than the Keihin PWK flat slide unit, called the Molkt. These are also around £20, but the similar dimensional issues apply.
I have bought one of each to play with & could post piccies if desired to compare them.
Given the bike didn't want to run, starting from scratch with a non-standard carb to try & get it running would most likely not be the best approach IMO. Substituting a "probably good" alternative OE carb that required no modifications to fit allowed an easy(ish) cross-check of the suspect carb. When the bike has proven reliable with the alternative OE carb fitted, other solutions could be applied from a "known running OK" basis.
Easiest long term solution is probably a reproduction BVF, around £50 from Ebay, which should be a straight "drop in" replacement. Second (more expensive) choice would be a Bing, which were fitted as OE on post-unification MuZ bikes. Availability of these seems patchy, though, & they were around £130 last time I saw one for sale on a German parts seller website - these also require a different throttle cable IIRC. Either of these solutions should just drop in and work - none of the development work that will be required fitting a Chinese carb.