Why go through the effort of setting up hose timers and irrigation line if I wanted to mess with a garden hose.

Oh I fully concur. I think I'm going to go the DIG injector route since there's only one section of my system that I'm particularly keen to fertilise regularly (annual chili peppers & tomatoes) whereas the rest is existing trees which already do fine with nothing, or occasional ground-dump granules.

For the DIG, if the intention of your first link is to go into the DIG, be advised that these are probably/almost certainly National Pipe Thread NPT, not Garden Hose Thread GHT which are semi-inexplicably different, which is bloody annoying. Therefore I think the move is these guys as you mentioned, plus these guys at Amazon or HD.

Oh, probably irrelevant since you said flowerbeds but just in case (and since I just saw this video about it): if you're fixing to grow edible fruits or fruit-like veggies, MiracleGro "All Purpose" is for vegetation, whereas this would be for fruit.

Cheers bud!