The main difference is that they do not use a pilot or main jet. They have a needle and what Lectron calls a power jet. You never have to remove the float bowl as the power jet is either externally adjustable or removable. The needle controls the slow circuit and midrange and instead of using a clip to adjust it, the needle screws in or out to change the length.
Lectrons have a bad rep as being hard to tune, but we have had no problems. In fact, once you get it figured out its actually easier.