Leo; I only just found the above board listing, have not ordered one to try out. But the price seems reasonable for a board and a 4 light crossing head, all for $12. Hard to beat.
While developing the original fixed-speed circuit back in Sept, I also did a variation using a small top adjust single gang trim pot to vary the flashing speed. Then I did a 555 timer version that also has variable flash speed. I ordered boards for each and they both work well. Didn't publish them here because it didn't seem like there was a whole lot of interest in being able to vary the speed. But if there is I can add them to the shared build files thread that rtr12 has running.