Pros
Good work-life balance. Decent salary for the area. Decent benefits. I hear good things about the non-avation-segments at garmin (Personal Navigation Devices, fitness, outdoor, marine).
Cons
Aviation is necessarily slow. Be prepared to work with tools that are well over 20 years old, mostly home grown. Most of management is made of former engineers. Unfortunately, most of them started as EEs and do not understand software. Most believe C is the ideal language for any and every problem faced in the field (actually, a few admitted to me they'd prefer to develop our customer facing GUIs in assembly language). You'll frequently get pulled of of your project for weeks at a time to help other teams test their code. This mostly means getting code coverage. There are very few opportunities for learning. Management makes no attempt to keep you up-to-date with the happenings of computer science or the latest tools/technology for engineering software. I can't recommend getting a job in Garmin's aviation segment unless you're prepared to spend your career there. You won't acquire very many marketable skills.