Time for a review of my Mason Definition. Since mine is a slightly quirky build, I'll talk about the frame, fork, and wheels first.

The Definition is a sophisticated aluminium frame designed by Dom Mason, who used to design bikes for Kinesis, and built from Dedacciai tubing. It's made in Italy, and finished to an extremely high standard. The smooth welds and tube profiles mean the bike looks more like a carbon machine than something fabricated from bits of metal tube. There are rack mounts and discreet mudguard mounts, plus clearance for at least 28mm tyres with guards. The full carbon fork, with tapered steerer, has hidden mudguard mounts and is Dom's design. The frame is designed for disk brakes, and the fork will take a 160mm rotor. Cable routing is internal, with neat blanking plates that allow Di2 builds, builds with cable operated mechs, and cable or hydraulic disks. There's a proper threaded bottom bracket shell.
The wheels, developed to suit the frame, are by Hunt: wide, tubeless-ready, light, moderately aero, and with notably smooth bearings. I'm running Hutchison Sector 28 tubeless, at between 70 and 80 psi.
How does it ride? Quick, light, responsive, and astonishingly comfortable. I find myself riding 100k or more without a break without a second thought. I tend to suffer from tingly fingers, but have not so far experienced even a hint of this on the Mason. The bike climbs well, even with me on top of it, descends like lightning, and shrugs off bumpy roads.
A loaded Carradice Nelson Longflap on a Carradice Classic rack mounted on the saddle has no detectable effect on handling.
I really really like it (can you tell?).
Mason offer a range of Shimano-based builds, or else you can buy a frame and forks, plus the wheels separately from Hunt. Which is what I did.
My Definition is built up with a 1x11 SRAM Force 1 groupset with hydraulic brakes. 38-tooth chainring, 11-36 block. Hope bottom bracket, Nitto Noodle bars, Nitto stem, Deda carbon seatpost, and Rivet Pearl saddle.
Why the single chainring? On my old Omega I spend almost all my time in the middle chainring, and the SRAM setup means I sacrifice one -- rarely used -- high gear and one and a half low gears when compared to the 10-speed triple on the Omega. The loss of gears at the bottom end of the range is counterbalanced by the zippiness of the bike. Though wide-range, the SRAM block has closely spaced gears at the top end and doesn't feel gappy. Having a single chainring makes for a clean-looking bike and is mentally restful, almost like riding fixed or single-speed. It also eliminates a potential source of mechanical problems. I find I like the simplicity of the single-paddle SRAM shifting system: just touch to shift up; move through 15 degrees to shift down. The drivetrain is astonishingly silent.
The SRAM hoods are ugly but very comfortable, and the pronounced 'horns' provide an extra hand position. The SRAM hydraulic disk brakes require little hand strength, have excellent modulation, and are generally silent. They don't rub, but in wet weather or on dirty roads will occasionally pick up muck and make a pinging noise for a revolution or two.
If you're looking for a lively mile-munching audax-type bike, the Definition is an excellent bet (and if you fancy a similar deal in steel, there's always the Mason Resolution).
I'm entered for the 2,100-km Wild Atlantic Way audax in June. As things stand, I reckon I'll be riding the Definition -- tremendous comfort ad the ability to handle poor roads, with zero penalty in performance. Says it all really…