The problem with the Jakobs elemental line of weaponry is that they are outclassed by a good chunk of non-elemental Jakobs firearms. While you can use them it is more of a “because I can” and not anything really efficient.
If the Greed were to spawn with a scope I would actually consider using it myself but alas, iron sights only. The unique effect I never found useful outside of Axton with his passives or if you intend on having your nose down your sights all the time and need that extra movement.
The Cobra is not an elemental weapon but explosive, and technically it is not explosive as the trait is what gives it its explosive damage when the bullet hits the target. With a purple 37-ish percent explosive relic it is actually quite the monster and being only outdone by the Elephant Gun in terms of damage, at least on Axton. I am not sure how Reaper affects it but part of me believes it does not affect it and I am too lazy to bother checking.
The Stinkpot…eh…the Stinkpot is unaffected by Reaper, cannot critically hit, is inaccurate, and personally I find it to be a piece of junk. While it can do somewhat decent damage to armored enemies any Jakobs that is accurate and has decent critical damage will work just as well if not better when you hit a Loader’s critical hit spot(s).
Out of all the Jakobs elemental weapons the Twister is the best due to the amount of damage it can do, but in order for it to outdo say, the Hydra, it has to have a shock elemental relic or some other way of boosting elemental damage. It has the potential to make enemies disappear but the “bullets” are slow and the shotgun is an ammunition hog. Still a really good weapon.
If you want to get the most damage possible use a purple Magic Missile and Legendary Siren COM. The key to making Jakobs weaponry into powerhouses is to ensure that your target is slagged all the time and while such a tip is a no brainer in regards to UVHM it is even more a necessity of Jakobs.
In order to survive with the Rough Rider you have to play VERY conservative and max out the Harmony tree (ignoring Recompense) otherwise you will get wasted if you go up against a handful of bandits. You will be playing a lot of Peak-A-Boo in the more heavily fortified areas. The only real time where you will be able to be super aggressive without nuking yourself is when Life Tap has kicked in and even then there is a very good chance you will be kissing whatever it is as your feet if you are not careful.