The lithium manganese cell chemistry is supposed to be safer than lithium polymer. They can be charged at 2C. They also have a lifetime pack guarantee. If for any reason you toast one of their packs you can return it and get a replacement for 2/3 the original cost.
I've used the smaller packs in my mini but have not tried the larger packs yet. I was going to order a set for my Gmade but they weren't the right size for what I was going to use them for. The mini packs I got were also slightly puffed when I received them direct from pfm. I haven't had an issue with their performance.
I didn't think they made a 5000mah pack. It may be old stock because they currently produce a 3800mah and 5800mah for high capacity packs. The 5800mah 3S pack is currently on sale for 152.10 + shipping direct from pfm.