Thanks to everyone that's contributed to the thread thus far. I never would have known that these pens and cartridges existed without you all sharing your experimentation and knowledge.
I've been scouting around myself for reviews and info on what may be the best long term choice of pen and the Sanofi AllStar Pro seems like a good possibility. It delivers 1-80 units and has loud, audible 'clicks' as it counts down which would be a good fit for me. Not exactly cheap compared to the Ali Ergo, so I'll leave that on the back burner for now.
In the meantime, I've got 40 cartridges and a Lilly Ergo II on the way from Ali Express which should get me up and running.
I also managed to pick up 100 x 29g/12mm needle tips for under £7 delivered which I thought was a decent price.
Link for those in the UK.
Something I'd like to ask about as a newbie is the speed at which the pen delivers the dose (Test C in my case). My hunch is that it'll inject a lot faster than I have been doing manually and that got me to wondering if any of you guys have run into any issues with the dose delivery speed being to high?