You would need to use some prefiltered clean water to clean any filter unless you can clean the dirty side without the clean side getting wet?
If you started out with a decent filter that included iodene resin then carbon, there won't be much left for the UV to work on. If you were storing it and you kept it in the dark with something like Micropur Forte in then it will be fine for 6 months. The only things that would be definitely left untouched are heavy metals, fertilizer chemicals etc and as far as I know the only thing to touch anything like that is a Brita filter, so you need to be sure your source doesn't have any to start with i.e. don't fill up from field runoffs etc.
The steripen seems like a good idea for insurance against dubious hotel tap water, or bottled water where you thought it maybe bottled a bit too locally for comfort (the back of the shop for instance!). If the bottle rim or cap underside was still contaminated however you'd be wasting your time unless you had a clean bottle too.
If you opted for just a mechanical filter then chemical treatment is cheaper and more reliable than something with batteries and a microcomputer!!
Or just boil it like everyone used to!
The other bit I'm not sure about is I'd heard the Steripen inactivates bacteria, rather than killing them. So left for long enough they'd repair themselves? One of the lab reports from their own site uses "inactivates" on one page, then quotes a "kill rate" on the next?