As Jon said, there are some weeds that are just not going to respond to anything. But others can certainly be controlled with commercial products purchased at home or garden centers.
This will be a bit lengthy, so bear with me.
There are 2 types of spreaders in common use for granular products such as weed-n-feed: drop spreaders and rotary broadcast spreaders. Each has pluses and minuses.
I personally prefer the drop spreader. Each pass can be aligned with the previous track far more easily, so you don't have missed tracks that end up looking like stripes. But you will have to make more passes since the coverage stripwidth is only as wide as the container on the drop spreader. And if the grass is long and/or wet, the openings at the bottom can become clogged thus preventing the product from falling out onto the grass.
Now the broadcast spreaders cover a wider swath with each pass, but the edges of that are determined by how fast the user is moving and by how heavy the particle grains are. So it is not uncommon to have gaps in coverage where there is no product applied, as well as too much overlap and areas that then get twice as much product as intended. A broadcast spreader is not as easily clogged caused by length of lawn or wetness.
Now, all weed-n-feed products that I have seen must be applied to a wet lawn, so that the particles stick to the growth. Those wet particles will affect the targeted weeds and that is the means of killing them. And, the lawn must then remain unwatered for a specific time so as not to wash off the particles.
Applying too much of the weed-n-feed is just as bad as over-fertilizing; you will burn out the lawn in all likelihood. Not a thing that I would recommend at all.
Most users of weed-n-feed don't read instructions, and so they don't have a wet lawn first. And now you're using a broadcast spreader that might miss spots, or you're using a drop spreader that will probably get clogged. so some weeds will likely be missed even when instructions are followed. And if it rains too soon, well you can't re-apply or else you will over-fertilize.
What I do for weeds is quite different from the normal weed-n-feed, and I am pretty happy with the way my weed control has been. I use a liquid product called "Bayer All In One Weed Control For Lawns", and I only buy the concentrate as it is more cost-effective when used with the pump sprayer that I already had for other liquids; there are other similar liquids from other brands, but I tend to stick with what I've had success with. The few pennies per application saved is a potential big expensive waste of my time if the other product fails to work.
Applied as per the instructions, it will handle most broad leaf weeds and crabgrass type weeds as well. The best thing is, if I missed a weed, or if one is truly stubborn, I can re-apply as per the directions (usually within a week even). Re-apply weed-n-feed - is a DON'T!
Using this liquid, I treat exactly what I want to treat, without fertilizing additionally when I don't want that.
