+1 to GATraveller - I would not consider tri-tp anything close to prime rib, but I do think it's exceptionally delicious.
To me a tri-tip is sort of like a roast that needs to be prepared like a steak. Reverse sear or sous vide are the best ways I've found to cook tri-tip, unless you have a deep pit (and if you're not in the San Joaquin valley you almost certainly don't).
If you overcook it (which is easy to do) it'll be quite dry. If you slice it wrong it will be the toughest thing you've ever eaten. If you nail it, it will be tender, juicy, flavorful and beautiful!
Look for a plump, thick tri-tip if you can. Often they'll be quite flat, and these are obviously easier to overcook. Make note of the grain BEFORE you season and cook. Often the tri-tip will be sort of roughly boomerang shaped, and you'll likely want to slice from the apex (the tip)of the roast down towards the tips of the wings. There may be one arm that's longer than the other that can be cut off after cooking and sliced independently (otherwise you'll have very long slices of meat).
Seasoning can range from S&P to something much more elaborate. Garlic can be your friend here in a major way! We used to cook tri-tip multiple times a week when I was younger and living in CA and a local favorite was to marinade in cheap beer + seasoning (Pappy's) overnight before cooking. You could do something similar with red wine if you wanted, but be careful if you get a thin one (it'll be overwhelming). I've also gotten great results from V8 juice spiked with kitchen bouquet.
I'll attach a couple of pics that might give a good idea of what i'm talking about above in terms of how to slice (including where to take off the longer arm). You can see the shape will change a bit during cooking.
Worst I've done is leave a prime packer brisket to wet age too long in the cryo in my fridge. 21 days and $70 later I had a rancid hunk of beef you could barely stand to be in the room with. I was so distraught I still trimmed it, rubbed it, and put it on the egg over night. When I woke up the next morning and the foulness could still be smelled over the rub and the smoke I finally admitted defeat.
The only good thing I did was not eat it or feed it to my friends/family...
Nice cook(s) here, congrats! 'Fall off the bone' tender really just means overcooked, so you can certainly get the with or without using the ol' Texas crutch (tends to happen faster w/ foil). A really nicely cooked rib will allow you to take a bite right out of the middle like in a cartoon without pulling all the rest of the meat off the bone. If that's where you're landing, you're money!