Pretty good boards, as long as your in they're small voltage range. DX recommends that you stay within 3.6V to 4.5V. I read that is because between 4.6V to 6.0V (which it can take up to 6.0V) it gets very hot. In my testing I used a small fan to keep the board cool so this did not affect me.
These are a great alternative to resistors, even though resistors are cheaper. The best thing to do here is order 20 of the 1400mA version and you can remove each of the black AMC boards and each one you remove will cut down the output current by 350mA. I tested this and it does work.
Where these boards beat resistors is that these give you a semi-regulated output. If you use resistors and alkalines (for example) the flashlight will never be brighter than when you first fire it up. After that, the batteries will start to dim. If you chose your resistor based on the fresh battery voltage, as the batteries start to drain, your output will drop. With these, as long as your voltage stays above about 4.0V you get the full output. The 700mA version should need a lower voltage and the 350mA an even lower voltage. So that semi-regulation is worth the extra money to me. I can't tell you how much time and headache direct drive / resistors / alkalines have caused me.
I definitely love a good boost/buck convertor more than these, but these things are not bad little boards. I thought others could benefit from these numbers.