They don't work very well with Mk5 standard reflector headlamps. Very poor beam pattern, to get more light on the road, you'll be creating a lot of glare towards other road users. Even if you don't care - the result is still crap. Automatic membership in chavland.
Other options
1) Retrofit original xenon hids.
2) Fit and align proper hid projectors in your current units.
3) Fit Hello or Depo projector lights for H7 halogens, use HID H7 kit.
4) Fit brighter H7 bulbs.
1 and 2 give you the best light pattern. 1 is expensive and needs coding. About £400 2nd hand including Kufatec adaptor.
2 requires some work with fitting, but can be better than oem. Stick with known makes, like Morimoto. Use a decent H1 HID kit with it, total about €230.
3 Not as good as 1 and 2. Beam pattern ok, not perfect. £300 new.
4) Cheap, but better than using a H7 HID with a reflector lamp.