To me, the attraction for both is having something non traditional and a little bit unusual on the wrist.
They are both creatives, in a sea of plain and ordinary (from a design perspective).
To that point MB&F is obviously much further out there in most of its pieces versus Urwerk.
Urwerk is almost boring by comparison (crazy statement maybe) but relative to a Frog or a Bulldog any Urwerk looks almost normal.
On the wrist I think overall Urwerk is more wearable, especially for a smaller wrist like mine. The HMs vary wildly, but many still wear well on the smaller wrist. What both Urwerk and MB&F have in common as regards to wearability is the lack of traditional lugs and so one can usually get a very snug fit on straps which will be flush to the sides or your wrist.
I may be corrected on this one, so others with more exposure to both brands please chime in, but in terms of finish they focus differently. MB&F will have more classical component finish, think anglage, black polish etc especially in the later HMs where more components/movement parts are visible. It’s traditional.
That is not the Urwerk approach, I think more emphasis is on an industrial like aesthetic (not on shiny bevels or black polish) and on case architecture.
Compared to the everyday watches we see here and everywhere, both are stand outs and clear statements.
Both were “Art for the wrist” before this current environment where collectors, speculators, dealers and auction houses have adopted “art for the wrist” or “art one can interact with and wear” as support for the crazy increase in market prices.