I decided against 1st flush diverters as this is an irrigation project and I have 1700 sqft of roof I'd need to wash - it came out to 85 gallons to divert. Basically I'd rather keep 85 "dirty" gallons than divert it.
(Example for a heavily polluted roof of 1700 square feet: 1000 square feet X 0.05 = 85 gallons to be diverted)
I figure between the gutter glove and the gravel secondary filter I'm going to catch most of the chunks. Plus I've been going back and forth on filtering the overflow from the first tank to the second. Upside if I did that I'd have 275 gallons of drinkable water right there. Downside that (slow sand) filter will certainly back up and overflow the system upstream during rains.
Then on the other hand if I need to drink the water one day I'll dip/pump water from the top of the tanks and run it through the ceramic filters I have.
I'm sorry, I'm not sure how much the gutter glove was exactly - it was a cash deal for some gutter removal, gutter install, the gutter glove and some miscellaneous pipe work. I seem to remember it was as expensive as the gutters.
I'm impressed with the gutter glove - it even catches the granules from my asphalt shingles. Plus on the upside you never have to clean your gutters again.