Wondering how they preform?
All depends what you are trying to achieve
They don't "perform" as such when compared to side draft options, as air/fuel mixture is going through a 90 degree turn
If setup properly then starting may be a little easier.
But its certainly not a performance option when compared with larger Hitachi/SU's, Weber conversions and TB's (that said other components must be upgraded to take full benefit of any carburation change)