[ps2cho]

Looking for a mild tune -- something moderate that keeps reliability.

I'm also reading about ECU locks, I guess I dont fully understand if this means my 2016 535i requires sending the ECU out, or how I would know what I can/cant do?

Any suggestions or advice on the route to take?
JB4 or a full flash tune?

[SWFLf10]

I personally run bm3 on my 535i. I recommend checking them out. I was stage 1 for quite a while before upgrading to stage 2 when installing a larger intercooler and high-flow downpipe.

[CoffeeBean]

Stay away from JB4 on its own. It's a piggyback system that just fools the DME into doing things. It doesn't behave very well on the N55 either. I've used MHD on an N54 and 2 N55s now. Performance-wise you can't go wrong with it or BM3. I'm not sure if you'd need an unlock, but the MHD app has a free unlock check function to find out. They're about to release a DIY unlocker too if you need it.

[Unspec]

Only real reason these days to go JB4 is for WMI integration. I recommend getting a proper flash tune like BM3 or MHD, and then adding a JB4 far down the road if you decide to go WMI.