Chips are located in the electronic control unit, and its the control unit that leads to more or less increased power.
I haven't yet seen any chip manufacture that has proven to beat the control unit, and gain more power than others.
Having said that, is it important that the chip manufacture makes good reliable chips, we have seen very poor chips on the market.
The first step when looking for chips is to look at the control unit and find the serie number. That number can and will tell you how much power you will gain, or at least can expect to gain.
Then, having the number in hand, do you need to look for a good manufacture - I have only heard very good things about Jim Conforti's chip.
He needs info about the control unit in order to find the right chip.
So in short - if you have a BMW with a good control unit can you gain very much in terms of power by upgrading your chip - and if you have another version of the control unit, will you never gain more than 5-15 HP.
Thats the fact.
Remember that next time you drool about all those additional horsepowers some chip manufactures claims you will gain by replacing the chip.