Hiya mate,
I'd recommend getting an small old paint brush (a 1 inch brush is perfect) so that you can work the Gunk into all the little caps that you can’t quite reach.
Also don’t do it on a warm day (not many of those this time of year I know), otherwise the gunk can dry in places before it has a chance to break down the oil.
I also recommend using it on an engine that has been driven fairly recently, as the heat from the engine softens any old oil on the outside of the engine, (but the heat can also dry out the gunk so its 6 and 2x3 really, but if you put a good bit of gunk on it shouldn’t dry out).
Don’t try and do the whole engine bay at once, Get the hose pipe out and blast the engine to get rid of the min bits of muck and rubbish, and then put the Gunk onto the engine. Work the Gunk in with the brush, the fluid will turn grey in colour as it breaks down the oil, (this is normal). Leave the Gunk on the engine for around 10 minutes (I think the contain says 5 but I always leave it on for a little bit longer), then simply wash off with the hose pipe, and admire the clean engine
Just be careful of any painted area’s, it says on the tin keep away from bodywork, but I’ve used it on my inner wings and its been fine, but it did start to take the high temp paint off my cam cover
HTH
Brian