From what I understand, the 77 MkII triggers are fairly easy to slick up with good results, but I liked the idea of an adjustable Timney. I've installed 3 of them so far, and I have been very pleased with them. I am not a gunsmith, but reasonably handy, and I did find it a pretty easy install. There is a "shelf" or "tab" on the trigger that you might have to file down to allow the safety to rotate forward. You need a small file to do it, and you just take your time, file it a bit, and try the safety lever. You may have to file and try several times, but you don't want to overdo it. It's not that delicate, so you don't have to be afraid of it. Just take your time. You'll be able to see how much filing you might need to do. I finished up with some pretty fine files to dress up my work, but it's not a contact point for the trigger, so you're not slicking anything up or influencing the trigger action at all. Your just removing enough metal to allow the safety to rotate over it. When done you try the safety and trigger to confirm everything is working right. But - Read the instructions - I'm just trying to describe what I remember, and the instructions are the authority.
Are they worth it? I sure think so. I like a good trigger and the trigger is the only improvement I feel the Ruger needs. I have a few 77's and have tested the factory triggers and found them to be in the 6.5# range, and not so terrible as people say they are. But, I like about 3# for hunting. I believe the Timneys are running about $75 now. If you know a good smith, you can probably get a good trigger job for that or less - so that is another option, along with cleaning it up yourself. I find that I really don't adjust mine much, if at all, after I set them originally - but it's nice to know that I can. They are very easy to adjust. I always keep the original triggers - maybe I'd reinstall it if I ever got rid of one of my Rugers - but so far they are keepers.