Full disclosure before I comment: I have a few friends who work for ADT as installers in both the residential (resi) and commercial (com) side of the business.
Of course they will recommend going through ADT directly. I do too, but for different reasons.
Going through ADT Sales means they will be able provide you the most up-to-date equipment and packages ADT has available. Also, they will look to schedule an ADT installer who is paid by the company. Yes, the ADT installers do receive paid commissions for any upgrade sales they make (i.e., you initially order a certain type of keypad, then decide to upgrade). But, unlike most third-party installers, they are getting a flat hourly wage based on union agreements.
I'm also leery of third-party installers, even the ones that claim to use "ADT parts." Many times these are remanufactures of defective parts or are older parts that have been toss-offs from other jobs. Example: A customer asks for a package to be installed which includes X number of sensors. When the installer gets to the house, only W number of sensors are needed. Installer now has U number of sensors left over. Six months or a year later, s/he gets your job. Your install uses that same panel as the one installed six monthes or a year before and it needs another sensor beyond what is in the kit for your job. The "extra" sensor from the past job is used. The problems are as follows:
- that leftover sensor has a battery that is six months or a year old which means diminished life before replacement.
- It is keyed to the other job. Thus, the sensor isn't on the original parts list for your job and may not be recognized as part of the install which adds headaches if you are trying to get something fixed later on.
- There is also the potential is there for the third-party installer to claim an added charge beyond what you are already paying for the added sensor in your install contract.
Before you go with ADT Sales, though, I would suggest to anyone to do their own home review. Count up all the windows and doors separately on the first-floor of your home. Window contacts are priced differently than door contacts. All first-floor windows and doors need contacts. You should seriously consider motion detectors for each room on the first floor.
If you don't have a connected smoke alarm system (alarms on each floor of the home including basement and one in each bedroom all of which are triggered if one senses smoke), I would definitely recommend that. If you can go for the heat sensor in the kitchen, that would also be a plus. A CO2 gas detector would also be beneficial.
Second-floor windows can have contacts put on them, but it's usually only needed if you have tall trees around the home with branches near the windows or if you have a porch roof with windows overlooking it.
Unless you have some significant art collection, a honking amount of electronic equipment, or you have a maid service come in to clean your place, I wouldn't recommend an internal camera system. Outside, unless you are in a secluded area, you don't need a camera system either.
I'd also recommend that you pay the added price and go for wireless contacts throughout the house. I'd also recommend that you get the cell service. It costs more for install and monitoring, but knowing that if the phone wires have been cut or are out because of a storm, the system can still get an emergency call to the call center, that is peace of mind.
Hope this helps.