Design and assembly was as advertised but mileage estimates were significantly overrated. I started with the smaller battery and struggled to get the expected range even with keeping the assist levels as low as practically possible, and/or even turning it off while on level grade. I later purchased the larger battery and now use the smaller battery as a backup for longer rides. In addition, the estimated battery level indicator and power management is not very well calibrated and cannot be reliably used to estimate remaining range. For example, you may have 3/5 bars, and think that you have greater than 50% battery remaining, but that rapidly drops to 1 bar (or may even die) as you start to climb a hill, only to go back to 2 or 3 bars when you level out again. This can be frustrating. In addition, when the assist is turned off, the motor adds a noticeable drag, and is similar to riding in a light sand. Aside from these issues, the product works well, and makes riding enjoyable again, even when using the least amount of assist. I just recommend you treat the battery mileage estimates as absolute best case scenarios when on a level grade and when using the least amount of assist. If your ride consists of numerous hills and/or you want to use the most assist, I would cut the estimates in half. I would still recommend the product if you are considering converting your bike (as opposed to a new ebike) to enjoy casual 12mph rides - just expect less than advertised range and plan accordingly. If you are looking for a high performance bike, that is going run 20mph for extended commutes shop elsewhere.