Gillane,
On past boats I have had two different makes, Plastimo 608S, and an older design of Rotostay.
I now have a Harken, which I have not yet used.
The fundamental design principles of all are the same, with the exception that some makes have a continous line round a sheave, rather than a drum.
Despite very large difference in prices*, I found that both the Plastimo and the Rotostay worked ok, with Plastimo having the advantage that it was much easier to maintain and repair, and also was not integrated with the forestay. i.e. if you buy a Plastimo, it can be fitted to your existing forestay, the Rotostay would need a new one.
Due to a fractured stemhead fitting my forestay carried away during the 2000 ROI, It was not too difficult to strip down the Plastimo unit and staighten the bent foils.
The boat I had then had a babystay; without that the mast would probably have come down.
An important decision to make is whether you ever want to change headsails, if you do a twin groove foil is an advantage.
Also note the difference between furling and reefing.
Furling, roll the sail away completely.
Reefing, roll away some of the sail and pretend it is a small jib, which won't set too well.
Some sails, e.g. the mylar laminated sort, can be furled, short time, but are permanently damaged by reefing.
I have not forgotten the other Gibb turning black.
*Prices Harken 3x Plastimo, Rotostay 2x,
Frank Marsden