I can't foresee any problems with using a 20W50 as long as you can see the words 'API SN' on the can's label.
Chances are it will be based on predominantly Group II 500N base oil with a relatively low level of VII polymer. The DI package it uses should be at least as good as what you might find in say a Group II 5W30 (the joys of matrix formulation!) and might very well be better as you often need an AO boost to get 20W50s through the Teost MHT-4 test.
I wouldn't worry too much about friction modifiers impacting on clutch slip as this oil probably won't contain that much Moly or GMO (if any). Even if it does contain some, still don't worry as results on the JASO Friction Test tend to improve, the thicker the oil gets.
In short, you will get an oil that is very resistant to oxidation, have a high HTHS & adequate ZDDP (so will be good on wear) & will shear less than many other oils (and even if it did, so what?). The oil should have an extremely low volatility & a low polymer loading so it should be brilliant regarding piston deposits. And it's dirt cheap so what's not to like (apart from fuel economy)?
Back in the early 60s, my cousin Malcolm gave me my first bike ride on the pillion of his red Royal Enfield. They were affectionately known as Royal 'Oilfields' because they leaked so much!