I can't speak to an outside company. We have done the Disney VIP tours, and I'd highly recommend them.
Any outside company will not have access to the things the Disney VIP guides do. All they will do is maximize the use of LL and paid ILL and come up with a plan to get you on the attractions you want to do. They do not have any special privileges.
Disney VIP guides transport you from park to park in a private van, enter parks (and some attractions) through "back" entrances, and take you through the LL for attractions without needing to "book" the LL. You can also ride multiple times in a row through the LL entrance (for almost all attractions - not sure about the new ones like Tron). They also provide water/snacks in the van (at least they did when we used them). If you want them to pick you up/drop you off at your Disney resort, they can do that too.
Pricing for Disney VIP tours vary from day to day. You can call to check the days you want to go.
Just wanted to point out the differences between the two.