I fitted a kit from simonbbc a few years ago, like others have said there is only one extra wire to attach. The main difference I noticed is how quickly it starts, less than one second of the starter motor turning on a warm day! If you don't keep your oil topped up the engine fires before the oil pressure light has gone out
Simon can also give you a different advance curve to suit any engine modifications, I think this was no extra cost but it was a while since I ordered it.
I was debating whether a circuit to delay power to the ignition for a second or 2 before it can fire would benefit the bearings etc.
1969 Four door Saloon Old English White 1275 with ported head and HS4 carb. Wolseley 1500 front brakes. Currently off the road with a leaky master cylinder!