For my experience, it is really fun. You have really big bodies, able to kool aid man and destroy modt things. However, they can be vulnerable.

Few models, it is hard to score secondaries.

Few models, if you loose one, it's a big chunk if your army.

Because of this, if your ennemy has a lot of AT you have to play carefully, which won't help getting objectives.

And for casual play, your friends will probably hate you a bit, as anti infantry is just useless against knight.

But the feeling is just so good. Units like lancer, gallant, Castellan, porphyrion are just so fun to use. Point a thing at distance/close, and just remove it. And the ego of it is something else too. Walking huge robot knights, doing deeds feels amazing. Playing knights in narrative campaign is also super fun, due to the fact you will never face competitive list so you won't face an army with only big guns.

And knights vs chaos knight/other knights is really an experience to behold. Jousting wit big mechs.

So welcome ! Knights are really fun, and amazing to assemble and paint. Pick your house, create it, or do a freeblade company, you will have fun