I don't know where people get the idea about "clone eyepieces"!
There have never been clones. Ever.
Clones implies that somehow these have been copied or the design stolen. There are only a handful of manufacturers of eyepieces in the world (nearly all of them in China), and there are only a limited number of eyepiece designs. Anyone can go to the right factory and ask for eyepiece X if the design is not under licence and the factory will ask "what casing design will you like and coating specs". That is it. This is why the Baader Hyperions appear re-branded under a number of different flavours. And NO, the Hyperions are NOT a rip-off of the Vixen LVW's. Totally different optical designs with the only similarities being focal lengths and a focal length colour coding system, but they are not rip off copies of anything.
As for the TMB's, they are made in the same factory as when Thomas Black was still alive. When Thomas died the factory dishonoured the contract they had and started making these eyepieces for themselves - and good luck to the TMB estate in making a claim against that factory...
The TMB Planetary Type II's were a revelation when they were released, being relatively inexpensive for the quality of optical performance and inexpensive to manufacture. Without the licencing restrictions on the factory, they could sell the exact same eyepieces at an even cheaper price. HOWEVER, quality control is now not the same
When you do get a good sample they can be excellent performers. But the failure rate is astronomical!
I bought the entire line from one supplier in order to test them all out in Newts, refractors and Catadioptic scopes, all 10 individual focal lengths. I also had four other eyepieces of these, so I had duplicates which allowed me to verify QC, so 14 eyepieces in total. Of the 14, 4 were totally unusable! These would not even come to focus, just remained a blurry mush. Sadly too is both of the 3.2mm were crap - a real shame as this would have been a good focal length for one of my scopes.
Of the two 2.5mm samples I had, one was rubbish. The other flaming brilliant, going toe to toe with the mystical 2.5mm Pentax XO with both outstanding in Newts and refractors. I was able to pit both EPs against each other. The 5mm TMB is just as good as the 5mm XO in a refractor, but whoops the Pentax's pants in an f/4 Newt - the 5mm Pentax just cannot handle a fast Newt.
Like I said, when you get a good unit these TMB's are excellent. All perform really well in refractors for which these were designed for. In Newts the pick of the crop at the 2.5mm, 4mm, 5mm, 7mm & 8mm in really fast Newts, like f/4, so with slower Newts the other focal lengths are less challenged by coma and perform well.
Curiously, the 6mm was the weakest performer from the Thomas Black era and continues to be. It will still do an ok job, but the other focal lengths are better performers, and you don't want to buy something knowing that it is just ok for the same money.
The pic below shows all the TMB eyepieces I used in my testing. The ones with the white band are the duplicate pieces. The crap pieces were put in the rubbish. I kept 5 of them and sold the others. I often use them with my lunar and planetary sketching and observing.
Also pictured is a 9mm TMB beside a 9mm plossl. The eye relief across all TMB's is the same generous amount as is the same big eye lens size, unlike plossls who's eye relief shortens and eye lens reduces as the focal length gets shorter.
Alex.
PS, I do not sell these eyepieces as the QC is just not good enough. I would only recommend buying them from Ebay because if you do get a poor sample you can get a refund.
For inexpensive eyepieces, these are really outstanding. QC lets them down though.
PPS: There is a way to tell if the TMB is from the time of production when Thomas Black was alive - those particular EP's have the focal length engraved as "mm". With the current, post Thomas Black, fabrication, the focal length is engraved as "MM" and the box they come in does not carry TMB branding.
PPPS: These TMB's are also available rebranded too! There is nothing exclusive about this design either.