Personally, I don't love either of them, but if it has to be one of the two I prefer Cozy n Safe.
The top tether on both of these is a bit of an issue in that the placement doesn't give as good support to the seat when rear facing in an accident, and if you choose to turn the seat forward facing then you won't be able to use the spin function with the tether attached, and it does need to be attached as it's a critical part of the safety features.
Usually I would recommend Joie 360 Spin or Graco Turn2Me as cheaper 360 degree spin seats on a budget, but both of those are a little bit more expensive than the seats you're looking at at the moment (about £130).
There is an Ickle Bubba 360 0-12 years seat which uses a different style of top tether (Y shape going round both sides of the seat) and a clip to make it easy to get LO out. That one doesn't have a forward facing harness mode, it goes straight from rear facing to high back booster. Again, I don't love that seat, and I'm not sure how it would last as a RF seat or what the fit is like as a HBB, but I do think it's a slightly better option than these two due to the style of the tether, and the cost is around the same (£110)
If your LO is 8mo then they might have a bit more time in their current seat and not need to move up yet, so you might be able to wait and see if the Joie/Graco seats go on sale at all, perhaps at Easter. Do you know what the limit is on your seat and where LO is in relation to that?
Also - is £100 a hard budget for the next stage car seat?