I have the motion slider 36 and i'd recommend it.
People on here don't give friction sliders enough credit (and yes I have used bearing sliders). Once you learn how to control it, you can get shots that look identical to ones shot on an $800 bearing slider. The shot at :56 is shot at 105mm and is still smooth.
I've had 0 issues with reliability, slides the same way every time. I've also had no issues with it in cold weather. My experience may be different because I have a very steady hand, but I still believe you can get away with paying $125 for a slider.
As far as length goes 24" should be fine, it's also more portable than the 36.
*There are a few shots that have a little bit of shake in them, but that is due to the cheap 30 year old tripod legs it was mounted on. The weight of the slider started pushing one of the legs down forcing the slider to jump a little. Start at :30 for the slider shots. This was my first day testing the slider out