They are much of a muchness. The Liverpool one linked is probably the better out of the three mentioned on this thread.
I have the GTi and it has some of the ease of use/safety features of the i-Spin, but is based on the R44 version.
Compared with the R44, the GTi has extra side impact pop out things (act as a combined brace/crumple zone) and a switch/button to press when you turn it forward facing to discourage doing this too early. That's literally it. Everything else is the same as the original 360 Spin.
The i-Spin (what you have) has the GTi features and also better handle placement to spin the seat, a less bulky insert, extra recline setting and memory foam headrest which offers better side impact protection.
All three have extended rear facing (up to approx age 4), suitability from newborn, several recline settings, isofix fitting, spin function, fairly compact fit, support leg, decent frontal safety score, adjustable insert which has multiple parts to remove to give a better fit at different ages, fairly tall shell meaning it fits long-bodied children.
If you're having it for a newborn, it's worth knowing it takes a bit of confidence to get a good fit for a newborn baby with this seat. I'd also install it in your car and check the angle with the newborn insert in and the seat fully reclined. If it's steeper than 45 degrees from flat, then it is too upright for a newborn and shouldn't be used - ideal angle for a newborn car seat is between 30-40 degrees, up to 45 degrees is OK.
Watch the videos on youtube by Rear Facing Toddlers, as she explains the harness and inserts very well - the harness on this seat has large, bulky pads which have grippy plastic rubbery stuff on the back. This needs to be placed properly over the child. If you simply fasten the seatbelt and then tighten it, you'll generally find that the pads "grip" onto the first bit of clothing they reach (which is the edges of their shoulders/arms) and the belts end up too wide in a V shape, sometimes not actually containing the shoulders at all, which is a serious problem. A newborn is often so small that the pads seem bigger than their entire body! But it's important to get the fit right. Their knees also tend to scrunch up when they are really really first born, so it can be a bit tricky to do a 5 point harness and not get their legs caught in it. A bit fiddly. Take your time and be patient. Don't be afraid to reach under the baby with your hands/arms and reposition them - you want to line their shoulders up with the straps. If they are getting upset and that is stressing you out, take a deep breath and give them a cuddle then start again.
You CAN get a good newborn fit in this seat - I've seen it done - but it's not as easy as it is in an infant carrier.
If you find the angle is too steep or all the adjusting sounds too much hassle you could opt for something basic like Joie i-Snug or Maxi Cosi Cabriofix (which should be compatible with your pram) or Joei Juva (which is not) for the first few months until baby has a bit more head control (3-4 months) and then move to the Spin seat.