"J. Douglas Mercer" sez:
Sounds attractive to me.
However, as the features of a unit increase, so does the cost.
Do I need a wiper or quartz sleeve?

Need? No. You may have to disassemble the unit to clean it sometimes if
you don't get the wiper. I didn't get a wiper, used my unit for about four
months, and it's still sparkling clean, so a wiper would not have yet made
any difference for me.

Should I use more wattage that I need?

It doesn't harm anything to use more watts. I'm actually using less, a LOT
less, than some suggest, with great results. But keep in mind that wattage
is relative to reflection, pond volume, unit volume, water flow, etc. If
you buy a unit with a reflective (aluminum) interior barrel, less wattage
will have the same impact. Slower water flow through the unit gives the UV
more time to act.

Also remember there are two different sets of goals. If you want to
disinfect the water (sort-of), high wattage works. If you merely want to
remove the floating algae and have clear water, a much lower wattage will
still work.

Are there features or brand names that I should look for or avoid?

The biggest factor to me is plumbing. Remember that if you're running it
inline on a filter or waterfall, adding the UV does increase your dynamic
head... so you'd want one with large fittings and a high flow rating. In
my case, I didn't want to splice that plumbing anyhow, and I have a
secondary pump/filter unit, an in-pond box, that I diverted the output
through a UV AquaFrog for; that's an option too.