I haven't actually used it, but it looks great except that their prices are somewhat higher than other 8051's. The old 8051 core had took 12 osc cycles per cpu clock cycle and the average cpu cycles per clock was 6. On the cygnal part the 1 osc cycle is 1 cpu clock cycle and the average instruction cpu cycle is close to 1-2 cycles making it a 20-25 MIPS part at 20-25MHz. It also has built-in JTAG debug, up 12-bit ADCs and DACs. I have not seen any 8-bit micro that has all of these features.