I just got some on sale at ralphs. Can I use it to make tacos? Like king taco tacos or will it be too tough. The butcher said "oh it'll be great." But, I don't know if he knew what he was talking about.
Marinade for 12-24 hours, or use a dry brine for about 6 hours.
Grill (or broil) at high heat.
Slice thin, ACROSS the grain.
Some people like it and some not, but depends on who's doing the cooking. I got some myself for $1.25/lb and am planning on making Pizzaioli in the fall with it. Husband thinks he hates it, due to how Mom cooked and served, but if braised correctly and cut against the grain, it's as good as anything. Don't know about "It'll be great" though!
This is my personal preference, FWIW, but I like shoulder steak rather than round for London Broil. As mentioned, London Broil is a preparation, marinated meat, BBQed or grilled, sliced against the grain (preferably done no more than med rare). Shoulder comes from the chuck primal of the cow, tends to have more fat, and as everyone knows, fat = flavor.