After trying an MT-01 a while back, I had the chance to ride an MT-03 today as a courtesy bike whilst my TenAir was in for it's 18k service.
This isn't going to be an in depth review as I only had the bike for about 12 miles.
First impressions then. It's stumpy, compact, small. Definitely small. I feel like I'm half the height from the ground that I usually am. Thinking about it, I may well be.

The engine sounds a little rortier in the MT than in the Ten, after having a nose around the back end I have come to the conclusion that they share the same silencer, so it must be the angle of it putting the outlet closer to the rider's ears and maybe the airbox is slightly more open. I don't know.
Either way, cracking the throttle and I'm off. The bars are really wide, and combined with the seat and tank position, make you feel as though you are sat right over the front wheel. The first roundabout catches me out and I find myself rowing with the bars a little bit mid bend. I'm used to dropping the Ten on it's side and then counter-steering quite hard, with the smaller front wheel and wider bars (yes really, they sure feel that way) the MT doesn't need the same force.
Next roundabout is dealt with in a smoother fashion and I'm rewarded with a skkrrsssh from the right hand side peg. Couple more roundabouts to go get the same results.
Deciding that hoodlum riding is the order of the day as I approach the city I try a wheelie from the first set of lights I get to. The front comes up a little on the power in first. Maybe an inch or two. Next set of lights and I sit a little further back and do a hip swing. Far better results and I get to second with the front happily lofted. I get one more set of lights to act the dick at and then I'm through the city and in work.

Heading back to pick the Ten up I give the little MT some berries and am rewarded with 101 leptons showing on the LCD display. The wind is plucking at me, but I resist the urge to crouch into it. I want to get an honest indication of what it will do. The basic suspension feels a bit choppy as we round a few bends at speed, and the bars amplify any movement from the front wheel. Slowing for a red light the front brake gets a good squeeze and I get the littlest stoppie going on. The brakes feel very direct, and I suppose there's not much speed to scrub off in most situations.
Aside from the more direct feeling of the front end, the bike feels differently geared compared to the Tenere. To get the same indicated speeds, the engine is at 5-600rpm more. What this means is that you are in second pretty quick from a standstill, and third is used pretty much constantly for trundling around the urban jungle. I suppose Yamaha have aimed this bike squarely at the commuter/first bike set, and wide bars aside, it feel like it satisfies hat brief admirably. I'm sure it would be economical to run, and the riding ergonomics definitely put you in a position of control, both mentally and physically.
All in then, a fun bike, but I couldn't live with one for longer runs. I think it would feel breathless once above 70 mph, which is strange, as the Tenere has another 15 mph before feeling a little bit asthmatic.
Still nice fun to try.