From my research into the subject most people seem to recommend the bellows over the blower, noise and the amount of dust generated being a big part of that. Mostly reading the American forums.
I just wanted to make the bellows type because I love the history and it is closer to the way they used to do it out on the goldfields. Call me old school but
the bellows unit just appeals to me
I also wanted a quieter unit and I am only considering using the leaf blower motor to run it because my brother had one available (someone was going to toss it out) and he spent time on it getting it going for me. I like to use what I have to hand and then improve on it over time if needs be. Also I was considering making a blower version later so I could compare how effective each is. So there is potential for reuse of the blower motor. If I can get my hands on a wiper motor I will try that as it should be a lot quieter.
The cost of a new Keene unit $2000 - $2500 is just way out of my reach right now.
I'm building the drywasher unit as a lot of the places I go only have water for a limited amount of time each year and it cuts the gold getting season short for me. Hopefully with this I can go out all year round.