GPS for iPad
There are currently four GPS that will work with the iPad (that I know of).
The first i the Bad Elf which plugs straight int the iPad dock connctor and is about3cm square. It uses the iPads batery and unless one uses an extension lead it is hard to place in a good position on an airliner with heated windows.
The next three are all bluetooth but Apple specific Bluetooth Protocol.
The first is the GNS5780. I had one until I left it on the glareshile. It was pretty good at acquiring and had very good battery life but had a quirky swipe strip to turn off and on and thye had major problems with being unable to swipe it off. It requird only a bare touch to turn it on, the upshot of which was it was easy to inadvertantly turn on when one put it in ones bag and thus was usually flat when you wanted it. I do believe they have now solved this issue.
Dual XGPS-150. Generally good performance though can really take some time to acquire position. Has a downloadable app which indicates satellite acquisition and battery state which was nice. Battery life good but one bugbear was that if not requested for position info for more than 15mins, it would go into a standby mode and then when asked again would have to re-acquire position. This is frustrting if one is in a descent with the STAR up on JeppFD for 20 mins and then on landing when selecting 10-9 Airport and expecting position info/ownship there would often be nothing. More so than in the air, it is on the ground taxiing that ownship really scores. Has a good positive on/off button function.
Recently released is a new GPS by Garmin Called the GLO. This is a combined GPS and GLonass receiver. It has excellent battery life-10hours plus and is really fast to acquire a position. It aso has a removable battery which is a standard Nokia BL-5CA phone battery which can be picked up cheaply as a spare/backup. There is unfortunately no app to acompany and the manual is pis poor-it seems you can only charge the device if it is switched on but nothing about that in the paperwork. It has a push on off button but again it is quite easy to turn on accidentally. However as the newest GPS available this one has been the most impressive it terms of acquisition time and battery life.