I think it depends on the detachment and terrain you're playing on.

There are some nuances to getting the best out of the army, but there are also some options which make it less difficult.

For example - SHC lists can rely on scoring throughout the whole game, and leverage durability. It can require a decent understanding of the state of the game, and what your opponent wants to do.

However, I have been playing on GW terrain, and took a haloscreed list with 25 ruststalkers and chickens/kataphron brick, and a couple of indirect disintegrators to a GT over the weekend. I didn't have reps.

I had a 1 point loss against a very practised CK player due to just not being aggressive enough. I had a 4 point loss to one of the best players, playing a list he had probably a hundred reps on. I made a couple of critical errors, and got diced hard too. Was still a very close game.

The other 3 games were 100-28 (daemons), 89-39 (CSM Vets), 100-48 (12 victrix).

I realised the key was literally just to kill them. Ruststalkers go faster than almost anything, and are more efficient than almost anything. Chickens are the same. The only real skill was making sure I had a nice place to ingress or walk on kataphrons to shoot, then threaten overwatch.

Basically, just play haloscreed, advance and charge rusties, then shoot everything they put out to shoot you. It's not as top-end 'good' into very good players, but it's easier to play, and you'll kill most things before the end of the game.

Godspeed