I fitted my Injen about 3 days ago and my answers are:
I haven't told my insurance about it. No interest as whos to say i knew it was on there as you cant even see it!
No you cant see it. Not sure why they supply a nice shiny pipe when you can see fook all of it!
Performance - high end yes, low end no id say (but haven't driven it an awful long way to tell)
As above, short rams are pointless.
Chris