I'm a bit biased, since I live way up in the north with the bush folk where getting my hands on batteries is difficult to say the least since i just can't order them on Amazon. Traxxas batteries aren't all bad. Best value? Of course not... But, if you already have them, you may as well use them till they die. No sense in throwing out a perfectly good working battery you already own just because we don't like the name on the sticker.
Those adapters are great and I still have mine. They come in handy when you end up closing your curtains, turning off all the lights and buying a RTR Traxxas rig in shameful secret like we all end up doing at some point. Especially when they come with a battery like the mini maxx and you don't want to toss out a brand new LiPo or use the slow USB charger it came with.