harmonyfarms, the backflow preventer protects the water source (City, well, etc.) against contamination and it is required by Municipal code in many cases; and rightly so, in my personal opinion.
The pressure regulator, to my way of thinking is a misnomer. When you connect the soaker hose, you MIGHT need to reduce the water flow in order to get an even distribution of water over the full length of the hose. I have found that by simply stopping down the control on the operational leg of the Y connection will achieve this. But then, the soaker that I use looks like "foam rubber" and comes equipped with a "fender washer" style of hose washer which appears to limit pressure/flow rate into the soaker hose.
Finally, I heartily recommend that you examine the Y connection periodically; they all get "limed up" and the non metal ones tend to deteriorate as time goes by.