I had HDR Brachytherapy as a mono therapy last June at Mayo/Rochester. Depending on which classification you choose I had a low/moderate risk cancer which was contained to the prostate. I was told they can target lymph nodes; this is a question that you should ask your radiation team. My treatment consisted of two procedures two weeks apart. Each session I had anesthesia, the wires were placed and left in for 10-12 minutes (depending on the dose needed) and I went home that day. Side effects were minimal, I was placed on Flomax for 30 days which was helpful, but I felt I could have got by without it (others describe more difficulty than what I had). I did experience fatigue 2 days after the treatment but was able to get back to my exercise routine by the end of the week. ED with all forms of radiation is a possibility. I am 10 months from my treatment and doing well with the PSA moving in the right direction.
I chose HDR since it was only two treatment procedures, the research shows it has one of the lowest recurrence rates, fewer side effects and quick recovery compared to surgery, and a well trained and experienced RO can place the dose exactly where it is needed.
There are some very good videos regarding HDR at PCRI.org that you may want to look at. It also never hurts to get a 2nd or 3rd opinion.