Harvest One Limited, through their Gadget Infinity web store, have been widely known for their Catus brand of radio triggers for "Strobist" use. The Cactus triggers were (are) an inexpensive way to get into off camera flash triggering with radio triggers. The earlier versions operated well enough under many limited range conditions but could sometimes be less reliable than desired. They also could be subject to radio frequency interference from newer flash designs that didn't want to play nice, like the Canon EX series. The basic design went through a number of changes and new models were released in order to address the reliability issue along with making the product more user friendly. While improvements were made the electronic design was basically the same but tweeked with every new version up until now.
The Cactus V5 trigger is a completely new design. Where the previous versions operated on 433MHz radio frequency the V5 uses the 2.4GHz band. Radio triggers that used the 433MHz band could experience interference and false triggering when used with RF noisy flashes. This could limit the already short range of operation for these triggers. In extreme cases (false triggering) they just couldn't be used. So the logical solution to the problem is to move to a frequency band that these noisy flashes don't radiate in. This is one of the reasons most of the recent triggers are now using the 2.4GHz band.
