Gan are widely considered to be the apple of speedcubing, they have released a lot of speedcubes which are significantly more expensive than their competitors, they have achieved a brand name which makes them stand out in the eyes of many new cubers who think that their cubes will give them excellent times simply because many top cubers use their cubes.
The reality is more complicated; gan cubes are not going to drastically improve your times, practice and learning new algorithms are the only way to do that.
While Gan initially only made 3x3x3s, they have expanded in the last few years to release cubes for quite a few WCA events:
Gan initially released a gan 249 and later a gan 249 V2, these 2x2x2s were not widely received and are not stocked on speedcubing.org at the moment. Gan have more recently released a gan 251M series which are regarded as excellent 2x2x2s, the Gan 251M pro was used by Kim Roger Hoyland Larsen to achieve a 1.32 average and a 0.57 single. Gan have also released the Gan 251 M Leap which has very strong magnets. Many top speedcubers still use the Valk 2M but this is no longer in production so is very difficult to get hold of, Gan 2x2x2s may be a good replacement now since the X-Man Flare was not well received.
3x3x3 is Gan's main speciality, they have released many 3x3x3s over the years and can be expected to release their annual flagship every year. The Gan 12 Maglev UV is still used by Tymon Kolasinski but Max Park uses a Tornado V3, Gan's previous releases such as the Gan 11M Pro are also still excellent speedcubes. Gan does have a few cheaper options such as the Gan 11M which is still a great speedcube and can be used to achieve excellent times, however, other cube brands have options which are competitive with all Gan cubes that are at far lower prices, Luke Garrett used a RS3M 2022 ball core for his 5.02 average which ranks him 4th in the world, the RS3M 2022 ball core is only £17 which is less than even the cheapest Gan cubes available.
The Gan 460M was not well received and is not stocked on speedcubing.org because of this, Gan tried too hard to make a 4x4x4 that feels like their 3x3x3s and it was a flop, I suspect Gan will eventually try to make a good 4x4x4 but for now the best 4x4x4 is in my opinion the Aosu WRM
The Gan Pyraminx is a competitive option and is used by some top speedcubers as it is very smooth, however, the Weilong Pyraminx is my main pyraminx. UK National record holder, Daniel Partridge, uses the YuXin Little Magic Pyraminx, he does claim that the new mould is not as good though.
The Gan Skewb is widely considered to be the best skewb on the market, competitors such as the Weilong Skewb have failed to compete, I feel the skewb is the one event I can say that the Gan cube is definitely worth the price tag, if you care about getting good at skewb then it is worth getting the Gan Skewb, there is a standard version available at only £18 too.
For some reason Gan decided to also release a mirror cube, the Gan Mirror M is undoubtedly the best mirror cube on the market, Gan have even released a UV Coated version! Mirror cube is not a WCA event so it is strange that Gan decided to release a mirror cube, however, it does end any competition in the event, the Gan Mirror is the only magnetic mirror cube on the market.
Gan have released some excellent smart cubes and have developed their Gan Cubestation app, the Gan cubestation app allows cubers to compete against each other in real time all around the world, Gan smart cubes such as the Gan I3 are still excellent speedcubes despite the technology required inside and allow speedcubers to achieve times very close to what they would get with flagship Gan cubes, it should go without saying though that Smart cubes are not allowed at WCA competitions. Gan have also released a robot which can solve a cube for you, however, this is mostly just a novelty and has little real use, especially as the fastest speedcubers can probably beat the Gan robot at 3x3x3.
So in conclusion, Gan cubes are sometimes worth the price and sometimes are not, it is important to do good research to determine what is best for you, it is possible to be world class with any modern speedcube though. I would recommend attending a speedcubing competition that I am sponsoring and try out a range of speedcubes to see which one you prefer, the best speedcube for you may be an obscure cube from a brand that may be less well known.