First of all ive also fitted the same HIDs to mine, also had to switch connectors but seems water tight as the seals are pushed together. I opted for 6000k. I had 6000k in my last car also and were very white to me, however these 6000k's are waaay blue'er than my last kit, i emailed the seller and sent him pictures and hes offered to send a replacement pair. but i might opt for 5000k or 4300k to be safe because i like them white too.
Its strange someone brought up it being legal when the IS is setup for HIDs, as it was a option, also all SE's do have washer jets? so cant see it being a problem. in addition i had HIDs on my focus and sailed thru MOTs which was not setup for HIDs. Scatter only occurs badly with old style headlights without defusers over bulbs, im surprised anyone flashed you because the IS is much better than my focus was at directing the light and have never been flashed with either. did you get 55w? btw just a warning, those cheap kits are OK, but the bulbs to tend to fail after maybe a year, you will find you will have to turn off and back on again to get it to fire it up, however replacements are a meer five pounds for a pair...