I'm not sure which iteration I have, but it's the bulky one in the black fabric case before the slim flat type. It's the first pedal assist electric bike kit I've had, and first impressions are great. The power take-up is really strong and even on its lowest setting, it provides a noticeable amount of power to the ride. On its highest setting, it will make cycling up steep hills achievable where otherwise at my age, I would probably have to walk with the bike Instead. There are some minus points too that need considering. 1) its important to aim at the lowest effective setting to prolong the battery. At full power, it won't last very long at all. 2) Adjusting the power on the move can be a bit tricky at times, so it's worth buying the handle bar accessory if you can. 3) Importantly, in hot sunshine the battery can shut down to protect itself leaving you with no power assist. Clearly, the black battery container absorbs heat very efficiently and the batteries create their own heat even when working moderately hard. This causes the system to shut down. Once it's cooled, it fine, but it can be a problem if you have to rely heavily on the battery to get you home. My solution is to unzip the case lid and this seems to work well enough, but it has to be remembered that it should be zipped up in any kind of wet environment. Overall, I'm happy with this system. I would of course like a bigger or better battery to extend the range, but that has to be balanced against weight (I chose the smaller battery on offer as I wasn't sure if the system was worth having so didn't want to spend the extra at that time to get the slightly bigger battery, given its cost). I'm now thinking of getting a more powerful system to get the extra range.