It kind of depends what your expectation is for the seat. The thing is that they say age 0-4 but the maximum size of child you can fit in the seat is based on a perfectly average four year old, on their fourth birthday. That means that about half of children will reach the limits of a seat like that before they turn four. Most of that half will get there somewhere the year that they're three, but if you're really unlucky with a very tall child who times their growth spurts wrong and/or a seat which just happens to be a bit smaller than average, some children will get there at about 2.5 years old.
Of course the smaller than average half will be fine and may even be able to stay in the seat significantly longer than four, but IME you can't necessarily predict the size of your children before you give birth. At least with the infant carrier, you know you'll only be using it while they are an infant, and have the expectation to upgrade it when they become a toddler or maybe a little before.
But if you're hoping to only have to buy one seat before you get to the cheaper, simpler, lighter booster seat age, quite a lot of people will end up disappointed. It is also handy to have two separate seats covering age 0-1 and then age 1-4 (ish) because most people tend to have children about 2.5-3 years apart, so it works well for passing down as you have about 12-18 months of the second one occupying the baby seat before you have to boot the eldest out of their toddler seat. But again if you're prepared to buy two toddler seats (or only want to have one child) it might not be an issue.
On the other hand - infant seats, especially the bases, are so expensive for what they are! I honestly think they see new parents coming - in America, it's standard to get the base free with the seat, even the cheapest infant seat. And if your aim is not necessarily to skip a stage of car seat buying, but simply to get as much use out of what you buy as you can, then I think it can make sense to look at a 0-4 years one, and when they outgrow that (or need to vacate it for a younger sibling) then you can decide what type of seat to get them next, whether you go for a basic high backed booster type seat if they are old enough and sensible enough or whether you want to get a larger harnessed seat for them up to 25kg (of which none are really suitable right from birth).
I will say if you've got maxi cosi adapters that opens you up to a load of possibilities, not just the maxi cosi pebble. Manufacturers tend to keep quiet about this because they want you to buy their own brand car seat, but a huge number of brands use the same adapters. I try to keep up to date, this is my current list:
All infant seats from:
Maxi cosi
Cybex
Nuna
Besafe
Recaro (nb, the Zero 1 elite baby seat uses an interim adapter)
Then also:
Axkid Modukid Infant (with interim adapter)
All Joie infant seats except Juva
Avionaut seats (there is one branded as Venicci Ultralite in UK - no other Venicci seats fit)
Cosatto Dock
So if you want a compatible car seat, you definitely don't need to pay £200/400 with the base - the cheapest one on that list is Joie Gemm, which is about £60-70, and there are two choices of base, seatbelt fitted for £60 or isofix for £90. It's a basic seat and you might prefer a different one, but it's an option. There is also a Silver Cross infant seat which might go on your pram without adapters.
Another "wildcard" option to look at is the Recaro Zero 1 elite, which combines a 0-4 year swivel seat with a pop out infant carry section. However, this is £400 as well. And I have a feeling you can't use the infant section as a standalone seat, so it is not much good for passing down to younger siblings.
One last one - if you want a TRULY premium and long lasting seat and can wait until September, there is a properly amazing car seat of the future being released called Axkid One. Rear facing, isofix all the way, recline right from newborn up to older child who wants to look out of the window, suitable up to 125cm/23kg (this is about 6-7 years old). It's bonkersly expensive at £700, but actually if you went for the £400 infant carrier then a £300 rear facing seat up to 25kg, you'd pay this much anyway! :o I wouldn't buy it myself, but I am genuinely really impressed at the concept, and for someone who knows they only want one child it might work really well.
