Personally I love using an injector or a brine pump. I tend to use injectors and brine pumps as a tool to help speed along the curing and brining process for larger pieces of meat(sometimes I just can't comitt the time and space for extended periods of time needed with some curing and brining). If you're using a liquid with nitrite you have a little more leniency in cooking temperatures but I reccomend your finished product to be no less than 160 degrees ( and not that much over either; I tend to pull at 155 and let it carryover cook some). The only difference between injecting and not injecting is purely based on what kind of liquid you use. I don't reccomend marinades since those are intended for smaller cuts of meat that would be better suited for the grill. I stick purely to brines and cures which of course drastically alter both flavor and texture of meats which are not brined or cured.
This was my Christmas "Ham" which I injected and cured for 4 days before smoking. In reality this is a pork butt that I trussed, cured and smoked but without the injection I would not have gotten a uniformity of curing in as little time. In short I believe an injector is an invaluable tool if used correctly. Happy Cookin'!