I've had my Mellow now for going on 2 months, but received it in the dead middle of winter so haven't had a good chance to get out and ride it until recently. I thought I'd write a quick comparison of my experience on the Mellow vs. Boosted V1 (1400km done)
History: Prior to getting my Boosted, I had never skated before in my life. After a couple of weeks I went from cruising a tennis court to skating the roads in Auckland, New Zealand. I did 1400km on my boosted in a year, and used it as daily transport when the roads were dry. It was a great board, and I ended up selling it when I decided to move to The Netherlands. I preordered the Mellow and 1.5 years later after getting over here, I had the Mellow finally (I actually had boosted v2 pre-order too, but mellow was going to deliver faster to eu).
In short: So I've gone from living in a stupidly hilly city, to living in the flatest country in the world.
The biggest difference: Riding a Mellow will actually teach you how to skate. After 1400km on a boosted, I didn't know how to kick a normal board, didn't even know how to foot break. Looking back now, this feels abnormally stupid considering I was riding in bus lanes and the such. With the Mellow, you need to kick to start, you need to be off balance for a moment. I had started riding a penny board around prior to my mellow, and I can say, there is nothing quite the same as kicking and gliding. With a remote, it just feels less (I don't want to be a hippy here) "free". Up until I got the firmware update, I would have picked either boosted or mellow, but this really makes the difference. It's like cruise control for your kicks and it just feels natural to me. To reiterate, I can now ride other boards - boosted didn't help me there, and to be honest made it harder to learn.
Rigid vs. Flexible. Boosted have turned their setup to the Loaded Vanguard. I love a flexy deck, and it makes a huge difference to ground shock. Mellow, you gotta pick your board here, but more flex comes with more risk of drivetrain damage. I'm planning on getting something flexy soon (if even just for the skating), so will test that out as soon as that happens.
Thinner Urethane. Due to the nature of drives, the back wheels have less rubber - absorbing less ground shock. If you've got slick asphalt, good for you. If you've got chip road, you might not feel your feet afterwards.
Lower rolling resistance. Okay, you can still notice the drag vs. normal longboard, but hey, if you run out on the boosted, you're walking. If you run out on the mellow, you can still actually kick the thing. Also, just don't run out of power and then this doesn't matter at all
Holy smokes that range. Endless mode = stupid long skate sessions. Most of the drain comes from accelerating, so by you doing the kicking, it saves a whole lot. Boosted = 5km, Mellow = 10km. That's just the honest truth here
That rattle though. This is still something i need to figure out the best way to resolve. Maybe a new deck, maybe some bungy cords, who knows. Since the boosted is all one thing, it's rattle free and no noise. Mellow on the other hand, yep, that rattle is real sometimes.
Belts vs. hubs. After 1400km, had one belt snap on boosted, so can't complain here. Time will tell on the hubs. To be honest, this battle is won on the rolling resistance
Power vs. Assist. Boosted had static power from launch which was nice but led to me not learning to skate. Mellow is just what the brand is - "Mellow".
Top speed. I haven't done it because I like having legs - but Mellow is up to 40km. Just..., it gives me the shits thinking about it.
Water. Compared to the V1, the Mellow is king here. I've ridden the mellow through some stuff that I'm sure has voided my warranty by now, and it just doesn't give a shit. The boosted V1, as soon as it smelt water, something decided to not work. I'm sure this is fixed on the V2 though.
Drive swapping. Hey, it's cool, I haven't done it yet and I think not many people will do this often. But the option is nice right? This shouldn't be a deal breaker in the scheme of things
Things I just can't compare
Torque. Boosted would get me up some crazy hills, always going faster than cyclists. I feel the Mellow would have a harder time at lower speeds, however once you're going I don't think there'd be a difference. Unfortunately I haven't seen a hill in 2 months since I haven't been on holiday recently (woo The Netherlands! - it really is that flat)
You might want to learn to ride a non powered board one day, you want to also be lazy and not kick, but travelling 2km on a non powered board is just too far. You aren't looking for something super aggressive, but you want to be able to keep up with the expensive boards and not be left in the dust. The Mellow is for you. You're going to love Endless mode, and you'll like to even shelf the Mellow and break out the manual for some fun times.
You want something that gets off the mark faster than the cars, you don't necessarily want to learn to skate (or you already can and/or you don't give a fuck), or you are just literally looking for transport and a hover board makes you look lame, then maybe the Boosted is better for you. The boosted is a well crafted board and a great company, but to me it just doesn't feel like skating, it feels like Powered Skating vs. Mellows "Power Assisted, but will still make you go hella fast" skating.
For me personally (everyone is different), the Mellow is king. I went from commuter to skater, and now enjoy my board even outside the times I'm riding to work. Either way, you'll love either board if you just want that last mile transport to be not a boring walk.