I haven't yet tested it with an ATTINY chip.
B4R generates C code and then compiles it with the Arduino IDE command line tool. If you have such a board then it is worth testing it.
The R comes from Arduino. Though B4R is not really limited to Arduino boards. It can be extended in the future to support other tool chains.
Yes, I know the thread is old, but I found it while searching for information about these lovely little ones.
I have a bunch of Attiny85 and not even all Arduino sketches works on them. You need to fit all code inside the 8192 bytes available, there's no crystal to handle timing and so on. Maybe it would be viable if one were to create a separate Core library, strictly for these tinycases, but that's beyond me.
Most things run perfectly on thse small wonders, but of course you have to take their limited resources into account.
I haven't tried with B4R with Attiny though as I am used to programming in C. And I really don't know if I will benefit at all from B4R, given my experience with C and Arduino IDE.