I recommend the outdoor strips because they already have a cover and therefore emit a more even light (humidity is probably only an issue if you do a steam sauna every time). Indoor strips are just 'naked' and need an aluminium profile and cover.
In addition, the Outdoor is brighter (but I don't have the latest generation of IndoorStrip).
Attention: Outdoor cannot be shortened or extended (Fix 2 or 5 metres).