I bought a Class 121 a couple of weeks ago. the new motor bogie is certainly very smooth, and does appear to be a 5 pole skew wound unit.
However, it is very easy to wheel spin the unit, and it does not appear to have much grip/traction. It's fine for the bubble car, but I was concerned about it appearing in other ex-Lima locos, the 3 car 101 springs to mind.
It may be that the this is down to a lack of weight in the Class 121, whereas looking at the diagram for the Class 59, there appears to be two fairly substantial weights. It also appears as though all 3 axles may be driven on the Class 59.
Pity they couldn't fit a couple of LEDs for headlights though. On the Class 67 the white LEDs are quite effective, even though there are no taillights or light above the cab. Still toying with the idea of fitting an Express Models lighting kit, but I don't like the idea of drilling and cutting what is now a nicely finished model, so I may just leave the lights the way they are.