I never see these guys, but I know they come once a month because:
1. They leave a card on the door
2. Since we started using them I have not had to deal with pesky weeds.
This is HUGE for an allergy sufferer like me... plus not having to deal with weeds gives me more free time to do something really useful, like play with the dogs or watch the Food Network.
The one-time-first-spray fee and the more-than-reasonable monthly fee is some of the best money I have ever spent to not have to spend half a day in the Arizona sun hacking down or pulling weeds.