Ventajas
The culture at NI is pretty solid. Everything is low-key, the R&D side has a lot of leeway and things are pretty low stress. People genuinely like going to work here. I make my own hours, don't put in much over 40 hours a week, and while it's not company policy I can occasionally work from home when needed. All the managers in my group have been great and give a lot of autonomy to developers.
Desventajas
You can make a lot more money elsewhere. NI knows their culture is great and that they have very little turnover, so they don't have a lot of incentive to adequately compensate long time employees. I've been here 13 years and could probably make 40-50% more at another company. Management is ultra-conservative. This has allowed NI to weather a lot of the recent economic storms, but there always seems to be some new future uncertainty which gives them the excuse to continue trying to save money. Vacation carryover is still capped at 40 hours, 5 years after the temporary policy was put in place.