First I have to give a big thumbs up to GLV. I own several and I love them. Currently I have (2) GLV2 5V and (1) GLV XL Mini using a Kick. I have also owned a GLV3 Mini which I bought on the forum and sold about a month later.
I love the design and quality in the GLV. It is a solid, well build unit with a military grade button and very natural button placement. The unit just feels really good in you hand and is built to last. The GLV mini was a bit too small for me and the feed system personally didn't interest me all that much. It spent most of its time on the shelf so I decided to pass it on.
I live just down the street from GLV and stopped in the shop often to talk with Jay and Sarah. With the popularity of the inexpensive tank systems, Jay suggested that the GLV3 feeders will be special order only. That may play into your decision.
I can't give you a comparison to the Volt since I have never used one. It's also hard for me to really talk about battery life given the fact that I rotate several devices in one day. I know when I only had one device (GLV2) that I was able to make it a day on a charge without problems.
If money wasn't an issue, I would suggest a GLV Mini XL with a Kick Module. I think it is the best of both worlds but it will cost you in the $200 range. Size wise it is the same length as the GLV2 5v and slightly bigger diameter. Since it is unregulated, you could run a 18650 and have extremely long battery life or use a 18500 with the Kick for VV up to 10 watts (5v or so with a LR Boge). I've only had the Kick for 2 days so I can't really talk about battery life. Out of habit I swap all of my batteries every other night. I charged up the 18500s after the first day just to ease them into the cycles.
Given your budget, I would focus on the Classifieds for a GLV2 5V. Be forewarned, GLV's hold their value. I have seen them around $120ish but I recall one going as low as $70 (it was snatched up immediately).
Again a big thumbs up for the GLV and I can't find a complaint. Great product and great people to deal with. FYI- Due to the manufacturing costs GLVs are usually on pre order and made in batch runs. Dependent on when you order there could be a wait. You may want to call Sarah or Jay and see when the next run will be.