I have a Definition and love it. It’s every bit as comfortable to ride as other steel road bikes I’ve had, although I have not specifically ridden the Strael to compare it with. There’s obviously a small weight difference too, half a kilo maybe, though my Mason is about a kilo heavier than the bike it replaced which was carbon.
I did consider the Strael and the ones I’ve seen in the flesh are lovely. To be honest it was partly stock and lead times that swung it, as I bought it during the COVID parts shortage.
Also due to their sizing I would have ended up with a 58T which looked rather gate-like in the photos. Curse of being tall I guess, but the Mason in a 58 looks better IMO.
They’re both lovely bikes, don’t think you will disappointed with either.