The Samsung Remote Test Lab[1] provides this for free (with limits)— they have a range of real devices (S5—S2, Notes, Tabs, even Gears) that you remote into and can install APKs, screenshot, and otherwise have full control over.

Somewhat unfortunately, I've found the connection fairly unstable, and they don't factory reset between uses (so unless you remove your APK, it'll stay on the device and configurations persist).

[1]: http://developer.samsung.com/remotetestlab/rtlDeviceList.act...