I have worked with some who have done short courses and many from apprenticeships.
Firstly, if you’re honest on site, say you are learning, listen, watch, learn and knuckle down to it, you’ll find you’ll be ok. Some people I’ve had from these courses have been really good. Some have been an absolute liability, because they have no ability to listen and learn and they think they know it all...... the same with some apprentices. Some have been lazy, thick, incompetent and totally useless.
It also, as with anything, depends greatly on your instructors, their ability to teach and get things across in a way that you understand.
So, the short answer is, these courses are good for some people and are a good way to get a basic understanding and basic working knowledge. Just realise you don’t truly begin to learn until you get out on site.
Good luck