Hi,
I am a Technical engineer at TRACKER. Its my job to supprt the OEM's. Only TRACKER Monitor and Horizon are approved for LEXUS, but TRACKER's Response is a really good product.
We are in the process of getting approval with the Response. The current drain on all are products are very low. (Less than 1mA for Monitor, Horizon and Response.)
The Response is GPS, GSM and VHF based. You can use a customer website to pull off reports and see your vehicle. Cost compared to similar products are cheaper as other companies charge every time you use the website or poll the vehicle.
With the Response you have to carry tags on your person. (little bit of a pain, but not that difficult)