Engine bay cleans - placebo or great?

Hi. I am thinking of getting one of these soon as, not to put too fine a point on it, my engine area is not the cleanest I have ever seen.

If I do get it done it'll be in a couple of weeks (about to get an injector replaced and a new rocker cover gasket, as there is some oil around this for a start and running down to the lower parts).

But... are they worth it? Is it snake oil?

I am not thinking of one of those £300 'carbon cleans', just a local one with a steam clean and degreaser etc.

Thanks.