Plasticote's great stuff for the hobbyist but I always find it a sod to get a good consistent finish on, even on simple shapes so I don't fancy my chances of doing the triangle joints without getting at least one bit I'm not happy with. And you can't cut it back effectively without putting a further coat on, or repair it easily if it's damaged.
Hammerite is another decent option, easy to spray though not all that durable, it chips quite easily especially around square edges. And very solvent vulnerable. Still, it's a very nice tactile finish if you use either the wrinkly spray, or use the smooth but shoot a dry coat on top of your last wet coat, gives a powder finish (and, helpfully, is easy to get a very consistent finish for!) though again, impossible to repair. I like it though it's more a fun finish than a serious one IMO.
2-pack in my limited experience on bikes (motorbike frame not pushbike) is hard but a little brittle, though not to the extent it's a major problem. Difficult to work with of course but otherwise very good…
Oh, and halfords sprays or similiar, just say no, they're fine for what they're designed for but cellulose is just not tough enough to last at all on a mountain bike. Put it this way, I resprayed a panel on my motorbike with halfords stuff as a rush job (a crash 2 days before a big event) and though it did look absolutely fine on day one, by day 2 it was scratched, and then it got chipped. Not by a stone, no, by a BEE. Now, if you think your mtb will never be hit harder than my bike was, when striking a bee at 100mph, perhaps cellulose is for you but rocks are harder and jaggier than insects.