Since purchasing these batteries a few years ago, the only concern I had was the massive price tag. It seems now they're a lot cheaper than they used to be, and so what could have been a disadvantage has changed. I was considering writing they're quite expensive as the disadvantage, but I noticed the price is much lower than the amount I paid for them.
I got mine to power a large Microsoft Intellimouse, a Logitec notebook mouse, a Microsoft mobile mouse, and a few household items, including clocks and other items. I bought several packs of these batteries, each a pack of four.
The life on each recharge appears to vary, depending on which items the batteries are used for. Sometimes the result can be the opposite of what one may expect, in this case the batteries last very long in the huge Microsoft Intellimouse, averaging about a year between each recharge, while they only last over a month in the tiny Microsoft mobile mouse. The closest to obvious explanation maybe that the mobile mouse takes only one battery, while the intellimouse takes two.
The charging time on the battery says seven hours, but I think it takes closer to ten hours. I got a uniross mains charger, which automatically stops charging and switches off the LED when charging is complete. I'm measuring the charging time according to that, but maybe the charging time is affected as the batteries get old. Since I never kept records of charging time when I purchased the batteries, I can't say anything for sure. Anyone who has kept such records, maybe able to confirm or deny this theory. One thing I can say is, NiMH batteries have better battery life than NiCd.
I think these batteries are worth buying, as long as the items you wish to power can run on rechargeable batteries. Not all item can run on rechargeable batteries, so be sure to check if you're not sure.
The current cost is about £9 for a pack of four batteries, or over £20 with a mains charger. The price used to be about £15 for a pack of four batteries, and I don't remember how much the charger cost, but I'd imagine it was slightly more than its current cost.