Welcome from Oklahoma. I wish we had Kroger's here, I like their stores.
I used to use a charcoal/small stick smoker. Now I use an electric because I got tired of watching and fretting over 20-24 hour smokes. Now I do briskets and Pork Butts stupid simple.
I guess I am not quite as picky as some people on my meat purchases, the last 15-20 briskets came cryrovaced from different sources, Sams, Wally world, or the local grocery store. I can not tell much difference other than some need a little more fat trimmed.
I smoked all by pulling them out of the frig, opening them up, rinsing, and trim a little fat if needed. I then heavily rub them, putting a couple tooth picks on the side inline with where I need to start slicing to make sure I am cutting against the grain and put them in the smoker set at 225' with a probe inside them. In general, 12lb takes about 18-20 hours, 15lb takes about 22-25 hours. Some pieces stay in the stall longer than others, you just never know how long it will take. An Internal Temperature probe is the only way to be consistent.
I wait till the beeper goes off at an IT of 200' for more sliced meat, 205' for more chopped meat. Then remove and wrap in foil to put in a towel lined cooler for about two hours, remove and slice, ready to serve the next meal or usually to reheat for the next day. We freeze the rest for quick meals
This is the base method for me, each of us have developed our own methods. We use a variation of
Jeff's rub, sometimes change a little for a different taste. We like Hickory for smoke.
I would not think the shape of the meat would make a lot of difference. Time to reach the optimum IT will depend more on the weight and the characteristics of that particular chunk of meat.
Good luck to you, and let us know how it turns out.