I used Omnican for a while. I didn't like not having the inner cap and I kept getting needle stick injuries putting the big outer cap on at a silly angle. I didn't like that I couldn't just put a needle on my pen before going out and that I had to fish about in my bag for the pen needle and go through the song and dance of attaching the needle when at the table in a restaurant etc.
I convinced my GP to switch me back to Novofine when I pointed out that I was producing three times as much clinical waste using the Omnicans because the outer cap takes up much more space in the sharps box and you can't re-use them (I tend to use mine twice, three times if I feel like living on the wild side!).
The extra cost of all those sharps boxes & disposal was way, way more than the cost saving of a box of Omicans vs Novofine.