I have never used the Bat amps, but have owned Quicksilver gear and can speak a little bit about the company. My amplifier experience was with Quicksilver' first amp, the MX-190. This amp was in the 160 watt range, big chassis, had a cult following, etc. Although I purchased the amp used, and had the amp for years, there was never a problem of any kind. The amp was ultra reliable, and through steady use imparted a Rock-of-Gilbrator-like sense of problem-free behavior. With regard to their later amps, Ive heard from users that their amps shared the rock-steady reliability that my amp had.
The sonics were exceptional for their time. In fact, when I got the bug to upgrade, I discovered that the MX-190 performed better sonically than many of the highly thought of amps that I considered. Note in testimony to my MX-190 and to Quicksilver, I sold my used Quickie back to the person who originally sold the amp to me! Ive only heard of that happening with Quad speakers.
An essential item to me with regard to audio gear is the company that makes the gear. What is the value in owning an amp if it is unreliable or if the vendor does not fix your amp in a resonable amount of time if there is a problem, or if the company ignores you if you have a question? Relative to those categories, some vendors are significantly better than others. Mike Sanders and Quicksilver provide some of the best customer service in the industry. In short, if you audition the Quickies of your choice and are pleased with the sound, I would not hesitate to purchase them.
Re. the 6c33c tube. I like the tube, but that means I like how some amps sound that use this tube--it is not just the tube that defines the sound nor reliblilty of an amp. In some amps that use this tube, the sound is more organic and realistic than I've experienced with other amps. As Justin_time mentioned, the sockets used in some amps that have 6c33c's require replacing periodically. This is not a tube issue; it is a design issue. I known of an amp that required the sockets to be replaced on a regular basis seemingly because the amp was designed with bias levels that were unreasonable. Whereas my amps from Joule Electra, with an obviously much more thought out design, were biased at a more reasonable level and the sockets never required replacement.