Companies sell fast chargers and slow chargers to address the consumer's often contradictory demands. Which one you buy depends upon your priorities. Or you buy both and use the one that suits your needs at the time. (The Ni-MH market has grown enough to allow some companies to sell programmable chargers. One unit to rule them all. However, that requires the consumer to RTFM. Let's save that discussion for another time.)
PowerGenix markets their fast charger as the "1 Hour Quick Charger". 1 or 2 AA's @ 1500 mA, 3 or 4 AA's @ 750 mA, 1 or 2 AAA's @ 700 mA. The manual says it will charge individual batteries but they "should be charged in pairs for optimal performance."
PowerGenix markets their slow charger as the "5 Hr. Fast Charger". 2 or 4 AA's @ 300 mA or 2 AAA's @ 100 mA. The manual says "batteries can olny (sic) be charged in pairs."
PowerGenix does not use the word 'slow' in their marketing, yet. Maybe they are saving it for a 12 hour charger.
Historically, a fast charger will have your batteries ready for use much more quickly at the expense of life cycles and a slow charger will allow your batteries to be discharged and recharged many more times (life cycle) at the expense of instant gratification. It really does depend on your priorities.
Ni-Zn technology has been around for awhile. The consumer market is in its infancy. We are the early adopters (aka guinea pigs).