I use Chemlawn. I have a little over 2 acres and it was less expensive for me to pay them to fertilize and keep the weeds down than for me to buy all the material at Lowes Depot. Plus timewise it was getting a little hard to keep up with treating 2 acres in addition to cutting it and spending time with the family.
I never got any of their optional treatments - just spring, summer, fall, winter. They call about grub treatment in the spring, and lime and aeration in the fall. They always recommend these - so don't think that it's something special that they "detected" on your lawn. We ignore the calls - caller ID is a wonderful thing.
I've used them for a few years and up until this year my lawn looked great. But this summer we had a lot of dry spells and lots of grubs. I estimate that I lost at least a half acre of grass to the grubs.
One thing that disappoints me about Chemlawn (and other services too) is that they consider grub treatment an "extra" service, meaning you have to pay over and above the normal treatments. Yet grubs are something that can literally kill large sections of your lawn. You would think that they would automatically treat for something that could kill your lawn, but instead they include treatment for pests like chiggers and ticks - nobody likes those, but the aren't going to kill the lawn.
I spoke with the Chemlawn guy that does my lawn when he came out to do a fall grub treatment (extra $) and he said that some people skip the summer treatment (just fertilizer) and use the savings towards the spring grub treatment. I would recommend doing that after my experience.
(You treat differently for grubs in the spring vs. fall. In the spring, Merit (aka Grubex) is used and in the fall Dylox is used.)
BTW, in regard to the local guy vs. Chemlawn/big guy issue, one thing to realize is that Chemlawn is actually made up of a lot of "local guys". Chemlawn often buys smaller local established lawn services and brings them into the fold (along with their customer lists). For example, the Chemlawn guy that does my lawn used to own is own lawn service and sold to Chemlawn.