Bought a G29 (with shifter) earlier this year and I like it a lot. My primary driving game is Assetto Corsa (must have game for PC imo) and it works extremely well with that game.
If buttons are a priority to you then the G29 might be worth it as it has more wheel-mounted buttons which is very convenient, especially when you consider that the G27 only has 6 wheel-mounted buttons and may require you to reach over to the array of buttons on the shifter.
I believe the G29 is pretty similar to the G27 internally, but the G29 has upgraded steering sensors.
The G29 brake pedal has a rubber insert to simulate a hydraulic braking system, the G27 doesn't have this but it can be modified. The pedals are fine, they aren't really realistic as the throttle and clutch are very light, but they do the job.
Aesthetics are down to personal preference, I think the G27 has a much cleaner look.
Remember, the G27 was released a long time ago and buying a second hand one may mean you're buying a 6-7 year old wheel that's been through a lot of abuse, however, you mentioned CEX's 24 month warranty so this may not be a huge concern of yours.
One thing I will say is that even though I like my G29 I do sometimes wish I bought a Thrustmaster wheel due to the belt driven system that both feels better and is way quieter (compared to the gear-driven system in the g27 and g29), so maybe consider saving for one of those.