My first Bluetooth GPS was the BT-308.
Good device. But the old one. And it has a very long start time - sometimes 5-6 minutes. I used it for 4 years. During this time, new chipsets was invented: sirf-III and later MTK. MTK is very popular nowadays.
A year ago I bought on ebay iblue 737 (MTK chipset).
And fell on its often problem - static navigation (or rather its problems). There are as follows: you start to go, but the chip sees it a few seconds later. Therefore, it reports position with little delay. Increasing update frequency to 5 Hz did not solve the problem. But this is compensates by its sensitivity. He catches satellites everywhere. Inside the car, under the car seat, in the house... Recently, I had to go with the old BT-308 - satellites lost between high buildings. With iblue 737, I already forgot about this. Very quick start. Economical - bluetooth switched off automatically if there is no connection. It allows longer working time from one charge. USB part is not soldered inside and used only for charging.
I read on gpspassion forums that new MTK firmware solved static navigation problem and semsons.com sells GPS with the new firmware. I stuck with iblue 747. It can work as a logger as well. Ordered device was received very quickly and then was tested. Static navigation problems seems to be fixed. No delays. Iblue 747 can be connected via bluetooth or USB . Economical. As a logger, it worked for 3 days on one charge and is not discharged. I did not try longer. Here's a log in Google earth