I would follow your retailers advice .. I don't use DIG regulators / filters but have repaired many leaking filters on the non pressure side of a system !! There are indeed filters / regulators that can be under pressure but the cost will most likely be higher. I am only familiar with heavy commercial brass units ... and they are expensive !

Good Day ...

Sure, the heavy brass pressure regulators and commercial filters are "expensive". Up to $50 for a brass pressure regulator and $50-100 for a commercial filter rated up to 400 psi. But compare that to buying and maintaining 6 sets of filters plus cartridges and 6 pressure regulators, all with those cheesy plastic fittings that love to strip when you try to connect them. The cheapo plastic Y-filters run $10-15 a pop and the cheapo plastic preset pressure regulators run $7 a pop. I'd rather pay $50 for one brass regulator that'll service the whole valve setup and last forever than $42 for 6 plastic ones. I might ruin one or two before the things are even installed--I destroyed the threads on a Y-filter last year and I'm not even a muscle-bound guy...

I've been wrestling with the drip irrigation issue off and on for almost a year now, still trying to figure out how to automate my drip irrigation zones. I've got 3 zones now and need to expand, automate, and make things relatively indestructible. The information on how to do these things isn't readily available.