First, let me echo Jolenealaska's comment that cast iron is lovely. I know my answer will probably upset some but please bear in mind that it is based on many, many years of experience, not on anything I have seen or read.
I have two sets of cast iron skillets / pots that belonged to my mother. One set is 80+ years old and the other is 50+ years old. I grew up watching her cook, using these pans every day. I learned to cook using them.
A truly seasoned cast iron pan has nothing to do with oil. While oil will prevent rust, if the pans are dried thoroughly and kept dry when not in use, they will not rust. True "seasoning" comes from use over time. The pans I have are as smooth as you could possibly imagine. This comes with regular use and thorough cleaning. I have actually heard celebrities on tv say that "seasoning (with oil) only works on old pans". There's a reason for this!
If you look at and feel the surface of any new cast iron pan, you will notice that it has a rough texture, pre-seasoned or not. In the true sense of a seasoned pan, a claim that a pan is pre-seasoned is really not relevant.
I always recommend that anyone looking to buy cast iron look for used rather than new. Any wear on the pan will get you to the point you want to be at quicker. Also it's much cheaper and it doesn't really matter if the pan has a grease build up or rust. That can be cleaned off.
I use my cast iron daily. With a well seasoned pan you can cook or bake most anything. I use mine for searing meat, braising meat, roasting, frying chicken, soups, stews, baking (cakes, cobblers, cornbread), sautéing, and anything else you can think of.
After use, I wash with dish detergent, scouring with steel wool or cleanser if needed. E.g. after searing meat. (I know scouring sounds harsh, but that too will help to smooth a rough surface or keep a smooth surface pristine.) I always rinse thoroughly with hot water and thoroughly dry before storing.
One other thing I wanted to point out about using oil on cast iron. If the pan is not used very regularly and allowed to sit (even for a week) the oil can become gummy or gunky and can also become rancid. In the case of either, the pan will need to have all of the oil removed.