My understanding is that both of those work really well. Anytime you can water the entire root system, but also let it have as much air as possible too, you're plants should do very well.

The 15 minute timers are ok, but you really want a cyclestat. They are more money, but you have infinite control overy the duration of watering as well as the frequency. (about $140). You want abou 7 minute frequency and 1 minute duration (depending), and you can't come close to doing anything like that with the cheaper timers included in those set-ups.

My advice: Get a good timer and build your own system. Those are very simple to build and plans are all over the place. You won't need a float if you get a good timer. It would probably cost abouty half, including the good timer.