Yes my opinion is openly biased...
The Yokomo likes to break arms. In MY experience, in the time that i've owned a pro4 and Cyclone( Note, they share the same suspension)< my friend driving the yokomo has broekn 4 suspension arms.
I'm still sitting on 0.
The SD looks like it has a higher CG than the Pro4. And here in australia at least, HPI parts are cheaper than yokomo parts.
Depending on the SD in question - the layshaft assembly is a pain in the ass to remove. The entire rear of the car needs to be pulled apart to access the layshaft and the spur gear. On the Pro4, you just take the top deck off..
Yokomo tourers are also known as "Brokomo"..
The suspension kingpins on all yokomo cars like to fall out. They always back out. My friend has gone through too mnay to remember.
Some Pro's for the SD:
Geargox access is much better than a Pro4. 2 screws and you're done. The gearboxes are split vertically so they just slide open. This is so much easier than the Pro4. It's fantastic!
A pro4 requires the top-deck to be taken off+ along with camber links (Pop them off) and shocks (unscrew).
Lots more screws...
The SD is compatible with yokomo drift parts! BLING!
To be honest - both cars are very fast and will serve you well. Your best bet is to go with local parts support. There's nothing worse than waiting and waiting for parts to arrive so you can run the car.
I'd still much prefer the Pro4..