The 1s runs on a MediaTek Helio X10 chipset, with 3GB RAM and 32GB storage (non-expandable). The phone is dual SIM, with support for LTE, along with Wi-Fi 802.11 a/b/g/n/ac, Bluetooth 4.1, and GPS. There is no NFC.
The software on the phone is Android 5.1 Lollipop, with LeTV custom UI on top. The custom UI runs pretty deep and changes pretty much every aspect of the UI. The launcher is the usual iOS style affair we see on Chinese brands, with all the app icons on the homescreen.
The notification screen is completely clear of any shortcut buttons. Everything has moved to the multitasking menu, which has shortcuts to apps such as the camera, calculator, flashlight, along with the usual toggles for Wi-Fi, Bluetooth, etc., music playback controls, and also the brightness slider.
Combined with the app windows, the task manager becomes all too crowded, and that takes a while to get used to. LeEco even went as far as changing the system font, which now looks like Helvetica, and it is consistent everywhere across all apps, even third-party ones.
Whether the customizations are good or bad is a personal preference at this point, with some people liking them while others are preferring stock UI. If you're in the latter camp, it's better to stay away from this phone, as there is nothing that resembles stock Android here. As for updates, it's not clear at this point whether the 1s will be updated beyond Lollipop but it's best not to hold your breath for it.
The performance on the 1s was quite satisfactory. Scrolling and app launches are smooth and fast. The 3GB RAM also helps with multitasking significantly. Even gaming performance was quite good, with the phone handling light to moderately heavy 3D games relatively well. The 1s is by far one of the best performing phones in its price range.