The danger of 3in1 stroller systems: Why a complete set doesn't necessarily mean a stroller combination that lasts
TL;DR: When buying an all-in-one-set travel system, take into account it may not be as long-lasting as it looks "on paper". Focus on the seat unit and an ADAC-tested car seat - any carrycot will do.
A 3in1 stroller set with everything for a child from birth until the end of stroller-needing days... This might sound like a solution for all your stroller needs. And it even can be that - if you find the right fit. Don't get, however, fooled by promises painted by the product descriptions (= marketing), seller pitches, and high weight capacities of the seat units. Yeah, everything suggests this is just what a newborn will be comfy in, and an older ~ 20kg child will be fine in - because, well, the chassis can hold up to it, they say.
When deciding on a combo of "all you can possibly need", be careful - mainly with those affordable, robust, oval-shaped stroller systems that mostly show off the carrycot configuration. Do you know why that is? It's because the seat unit is much weaker (not talking about 'not that pretty' yet). The cheaper, often Polish-made stroller sets are maybe bulky (and heavy), but driveability-wise, they are quite nice with a newborn in a bassinet. And I even hear, see, get - raving reviews of how nice the pram is... 9/10, all great for the price... UNTIL the parents pass onto the seat unit configuration, and then, after a few weeks or months, sell the system. That is because it is impractical: to fold (even bulkier than before), to push (the center of gravity changed and now, with a cheaply made seat and a heavier, older child, the maneuverability suffers greatly), to put the child in (clumsy or breakable harness + very little space in the seat or for the legs + hard, weakly padded backrest...). It's just (often) not going to be comfortable with the seat anymore.
The same, in any case, goes for any other type of system of combination. If you don't see much more than the carrycot setup on the promotional pictures, there might be a problem. Ten pics of the stroller with a carrycot and one with the seat is also a not-ok ratio. ALWAYS pick your stroller system based on mainly seat unit - pushchair configuration. A pram, where the main goal is for the baby to lie on a rigid flat surface of the carrycot, will be absolutely sufficient in almost any shape or size. The seat, however, can claim any weight capacity in the world. If it doesn't have a backrest high enough, or a leg rest spacious enough for legs a little bit longer, or has a canopy very low... it will just never accommodate a child over a year and a half comfortably. That is absolutely ok if you buy the model anyhow, knowing you don't need it to last that long... One and a half, two years is the age of passing on to a lightweight, forward-facing stroller so much more practical for older children. BUT! If you are choosing your system based on a description claiming 0-3/4 years and actually wanting that one set to last the whole time, the seat unit and its measurements need to be above average, mainly if the seat is reversible.
Another thing is the car seat. Please, in this case, where the car seat is the only thing actually helping to protect your child in case of an accident. The 3in1 sets often have car seats, even those matching in color, but there are many sets where the car seat is of an unknown brand with no safety rating. These are in the sets just for some car seat to be there, and it looked good and full and "for any need you might have, while affordable". Don't buy these - ask for a 2in1 set of chassis, carrycot, and seat unit, plus adapters for well-known brands. And buy a good car seat separately. Almost all good and mediocre brands offer Maxi-Cosi/Cybex type of adapter sets, and you can't really go bad with Maxi-Cosi, Cybex, Nuna, Kiddy all fitting these adapters.
I find this very important. I mean, you may be the most careful driver ever, but If a drunk sits in a car and hits your car... you can't do much then, just to be properly belted in and use a car seat that is proven to be safe. That is ensured by a good ADAC test, which I suggest you always googled for when choosing a car seat. If you don't find it, just move on.
To sum it up.
Think, before making a purchase, about whether you want your stroller system mainly for the carrycot, and don't mind not using much the seat unit... Whether you want the seat to last you long - and if so, if it's spacious enough... Whether the stroller is not too bulky to be practical even for basic folding and unfolding into the car boot... and whether you absolutely need a color-matching car seat, or you'll rather protect your kid in one with a good ADAC test result. Then, look at the offer with clear eyes and objective, and choose from the right candidates ;-) Easy enough, innit?