Timing is the key. the late August/early Sept sprays are more effective since the 'flush' ends to be more consistent, and it knocks the plant back before going into winter, so it can't make anything to get through. The trick is to just try to keep up in spring, make sure you get the fall one right, then it should be easy sailing for a couple years.
You need to spray when the weed is still 'on the way up' so to speak. 3-way products work by 'growing the plant to death' so you an still see weeds to go seed after spraying if it's too late. A well timed spray is always great (i.e. Saturday morning, don't see anything, by noon see a yellow flush, spray ASAP) where by the next day you see the dandelion death spiral. All that energy has been put into getting it to that point and then it can't convert it to seed, even if the weeds are still unsightly for a bit.
One of these
https://www.homedepot.ca/product/hdx...yer/1000755742
Plus Killex concentrate you can also by at home depot: 50mL/sprayer full would give you the same active ingredient rate as the ag/professional products like Par 3 and Trillion (exact same ingredients, just half the concentration). That said, always follow the label rate and what not. But that's as cost effective and reliable a setup as you'll find, and can effectively spot spray to make the product last a really long time.