Tomball is pretty safe. The danger zone will be when you leave the airport over to I45. Not sure its an option but if you can get a toll tag in your rental car it will make life easy. Go west out of IAH, get on the Hardy Toll Road going north, exit onto the Loop 99 toll road heading west and that will take you right over to Tomball. If you're going to Baker Hughes take 2920, other Tomball stuff you can go to 249 and north.
If you don't take the toll roads then all the way over to I45 is sketchy, and then north from 610 up to Loetta is daytime okayish, further north the better. Night time, head on a swivel.
The other mild danger zone is south of 99. Again daytime probably 100% ok, night time mostly be alert. North of 99 is mostly suburbia, a surprising amount of pasture, and some nicer areas. Parts of what I consider the west side of The Woodlands is actually Tomball.
Tejas BBQ in Tomball is very good. I prefer Corkscrew in Spring, which is right off the Hardy. Tejas also owns a burger place on Main Street in Tomball. Never been. Mels in Tomball also has really good burgers more of an old timey place.