When I ordered my machine I bought some B400 to practise with. I didn't expect it to be much good but it surprised me and I do actually use it on my rackets now. I've also tried their B200 which also performs well and looks quite different to most strings due to the gold flecks running through it. Looks great on a black racket!
I ve already restrung rackets with B75 and Speed 70.
Speed 70 definitely is a "BG80 or VS850 type". Has a rough texture and the behaviour is almost the same. Has a crisp touch but a more solid feeling. I dare say it is a very good alternative to BG80 at a lower price.
About B75 it is definitely a "BG65 type". I ve never played with it but I ve so far made some restringing, and reached 28 lbs without problem.
What I ve noticed is that the has a lower elasticity (stretches less than BG65 and I always have to use the starting clamp to help me pull the last cross).
The stringbed becomes stiffer and it seems that the racket was strung with higher tension than the required. I advise to string 1-2 lbs lower in order to have the same behaviour (assuming BG65 as a reference).
About durability I cant say much so far, only by seeing the custumers rackets, after 2 weeks training, that the string is absolutely without scratches, like new.
So far, so good.
I finished the 2 reels I had (speed 70 and B75) and the customers never complained.
I applied tensions between 25 lbs and 29 lbs and the strings just behavied fine during the job.
About durability I just say that they arent behind of the "top" brands.