Now that I have almost a day on my new mini & Grande, I guess I'm an expert... just kidding.
So far, I'm not finding much a a delta in performance. I did briefly try 6v in my grande, and proceeded to fry my carto in seconds... yeah, I don't yet know much. But they both hit very well, and the mini's performance leaves nothing left to desire. It rocks. The Grande will be especially nice, once I find my all day Juice. For now, as I switch juices out a bit, I can't even see myself filling a whole 6ml of anything. Having said that, the the Grande is still amazing. It will sit on my desktop, and I will always know it's good to go. I won;t need to surround it with carts/bottles/napkins/batts/etc. This thing just keeps going.
If I had to pick one, however, I would so far say it's all mini. I wasnlt prepared for the difference in size, until I saw them in-person. I find the mini to be a pocket-friendly size, but the Grande is too big. So, I would say get both. If you can only get one, and mobility is important, you might want to think mini. You may, however, have to carry around an extra batt & bottle, that you wouldnlt have to with a Grande. But I'm really too new to know.
One question for you Reo Vets - what do you do about door "slippage", when pocketing your mini? I love the magnet door, but am so far finding the fact that the door slides, when I pocket it, to be a bit annoying. Does anyone have any tricks & tips on that that they could share?
Overall, however, I love both of my new Reos!