Is M.2 worth it for ssd for os drive and some program drive?

Depends what you mean by worth it. The m2 gives you serious bragging rights, as it is one of the fastest drives available, and in the right system can enhance performance.

On the other hand, from a simple value proposition, it is quite expensive, and there are plenty of more affordable ssd's out there.
 

ThomasLeong

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May 27, 2013
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For one, it saves hdd slot/cage space & is cable free, so less potential for cable problems now or in the future. Certain models are definitely faster than the normal SSD (if you need the speed), but it comes at a price.

Reliability? Too new to tell. In the 6 months+ that I've used one, there has been no problems at all (Plextor PX-G128M6e without the PCIe interface).