UV does exactly what you say: reduce green water. It does not serve
to do the bio or mechanical filtration that is also needed. If your
pond is well planted, you may benefit from the UV only at the start of
the season. Our pond, for instance, needs UV for a couple of weeks
right at the start of plant growth. After that, it is not needed. We
learned that after several seasons of running UV all season. Big
savings and loner bulb life come from just 2 weeks!

We prefer the seperate UV as our filter is a set of berm ponds rather
than a mechanical filter. We have not looked at the combination
units. I would think through whether that really suits your purpose,
whether you can operate one without the other, whether seperate
placement would be more convenient, etc. Other ponders may have
better advice on those things and on units they are using.

My _impression_ is that the units are not at all standard for ponders
here.

Jim