I did know it already before i'd got a Bosch pedelec.

In my opinion converting a bicycle is only a compromise. But the vivax Assist would deliver good quality for that compromise.
Since it's a austrian company i have no doubt about quality or life expectance.
There are many recommendations by existing users. I guess it's far the best conversion solution available.

Pros and cons are easy to find out. How exactly do you define good?
For commuting i would choose a bosch pedelec. Also because of the larger scaled battery system (up to 1.000W with dual battery configuration).
It's like a model train, do you want very small size with limitations or maximum flexibility with an universal solution?

I have not used vivax yet.