Arduino legal concerns and MTBF

Scenario:

I plan on using Arduino Uno in my business. Basically, my clients are using expensive devices for their operations. I will replace those devices with Arduino, and charge them.

Question:

1 - Will there be any legal issues with this?

2 - Off topic, what is the Mean Time Between Failure (MTBF) for Arduino Uno. How long should I expect an Arduino Uno to keep running if used 7/24?

Thanks.

1 - Will there be any legal issues with this?

Between you and Arduino (the company)? No; that sort of commercial uses is pretty explicitly permitted.
Whether your customers will be happy with cheap hardware is a second question.

2 - Off topic, what is the Mean Time Between Failure (MTBF) for Arduino Uno. How long should I expect an Arduino Uno to keep running if used 7/24?

Ah. Good example. As a "development" and "educational" board, I don't think that the MTBF has been calculated or published for any Arduino boards. There is not much ON an arduino board, so I'd expect them to last a long time, assuming that they worked to start with. But ... calculated and documented values are unlikely to be available.

I reckon the principal cause of unreliability on an Arduino Uno or Mega (or similar) will be the connections to it - especially if subject to vibration or a moist atmosphere. Soldered joints of screw terminals should be more reliable.

Getting a custom PCB made with an Atmega 328 attached (or the MCU of your choice) would probably be wise for a commercial project. The schematics for the Arduino boards are published.

...R