I switched to Flogas about 3 months back, its quick, easy and simple.
The whole operation of competition in supply is a virtual market, Bord Gais still operate the network that transports the gas to your house/premises.
So my dealings with Flogas have been minimal, basically all that in reality changes, is your billing comes from Flogas rather than Bord Gais, so if there is any risk, then its down to billing, and I have experienced no problems there.
IMHO its a no-brainer to switch, Like ESB on the electricity side, Bord Gais have one hand tied behind their backs at the moment and cannot compete with Flogas on price, the only reason for this is to carve up the pie before real competition starts.
One way of looking at it is, that while we wait for true competition, ESB and Bord Gais customers are subsidising the carve up, why pay ESB / Bord Gais ~10% more for excatly the same Electricity / Gas delivered over excatly the same networks?