I have both. Not sure why the hard lid even exists. Maybe just cheaper to produce in competition with the more preferred Vitamix. My hard lid just sits rather loose on top. I use it for seed, grain, Parm/romano cubed in chunks and powdered like snow---take some out when a bit sandy for a different texture. The fluffy snow is great for popcorn. I do keep a parm chunk for shaving and if I want hand grating.
I use my twister jar 90% of the time. It comes with a hard twister and a soft top.
I use it near daily or at least 3-4 times a week. Small batch humus, dressings, soups like roasted garlic/leek. Plenty big for two servings.
If your hard lid is much easier to remove like mine---it would be suitable for adding things as you go I think. Open/close fast. My soft lid is so sturdy but needs a good push and two hands to get it off. Mine has a cap and hole in the middle for adding oil and such.
Guessing the variety of lids is ease of use?
I purchased the twister jar 6 yrs ago? Or whenever it was first available. It died 6 months ago and a bugger to pay another 129$ for another. I checked E-Bay for a couple months and got a new one with a Blentec base with low mileage for 50$, (20 shipping) but nice to have and extra spare base for traveling. Probably take it to the beach house. 
For those having a annoying chore of getting thick ingredients out of any blender jar---leave the 2-4 tBsp in the jar and add a 1/4 cup of AC vinegar or what makes sense. A bit of toasted sesame seed oil, fresh ginger....more lemon, an herb...and ice cube for emulsifying...excellent salad dressing for a few days and cleans out your blender jar.
The twister jar has feet that you spin when blending.
