I think you probably need someone who's done it in the US to answer you.
I once asked an old lady about her prison ministry, which began many years ago. She came to the Lord late in life just after her husband left her, and met the Lord soon after. Then she was invited to visit prisoners, and hasn't stopped since. She reports that her first encounter was with a few lads all together in one room. Smiling, she took a deep breath and asked, 'Well boys, what brings you here?' I've always thought that was a brilliant opener, because it gave them the opportunity to be heard, and gave her the pointers she needed to make the gospel relevant to each of them.
I've read some horrific things about what happens in prisons, and it certainly seems to be a place where some people can lose hope very quickly, and become suicidal. This - and the loneliness that some people feel keenly, through being isolated from friends and family - would seem to mean that you will probably be welcome at heart level, even though you may feel frustrated by some of the safeguards, while at the same time as appreciating the reason for them. I'm sure you will be challenged by the number of career criminals, and kids from 'criminal' families who just go round and round the system. I met guys who felt safer in prison, so every time they were released, they were aiming to get back in asap, as they had nothing going for them outside. Sorry. This is a bit bleak. There are, of course, men who meet the Lord in prison, and go on to serve Him faithfully.