I own a top flight acoustic piano and professional digital keyboards. I searched everywhere for a portable, super light-weight keyboard that I could carry on when flying/traveling to use for practicing and composition. The Casio CT-S1 fits the bill well, with a few very minor nits.This keyboard weighs in at less than 10 lbs. yet is very well built and 'feels' sturdy and solid. It's physically impossible to have weighted or semi-weighted keys on a 10 pound instrument, but the key bed is otherwise very good. The keys are nearly full-size, have a matte finish and a good touch sensitive response.The body of the keyboard is well constructed and does not feel fragile. The 'retro', minimalist look of the instrument with the cloth covered panel across the top is easy on the eyes. There is a built-in handle which allows carrying around your house or hotel with ease. It comes with a external power supply, but also runs on batteries. I sprung for a set of AA rechargeable batteries, worth the investment. Nit #1: You'll need to purchase a sustain pedal - not included.There is a very good and wide range of sounds, most important of which are decent acoustic piano, electric piano and organ voices. A nice feature is a set of physical buttons and a volume knob across the front panel. There are dozens of additional sound and tone controls accessible via the function button and the piano keys. Nit #2: I would like to have dedicated buttons for the most used functions: transpose, octave shift and reverb.The built-in speakers are very serviceable. There are 1/8" inch stereo IN and stereo OUT connectors, so I carry a couple of 1/8" stereo patch cables for connecting my Klipsch Groove bluetooth speaker (sounds great), tablets, phone, etc. The USB MIDI interface is ideal for for writing or transcribing music.Nit #3: The Casio case for this instrument, when available, has an awkward design (load from the end ??), and has questionable padding for travel. Casio would do well to make available a decent, well fitting, padded case - even at half the cost of the keyboard, it would be worth it. I scoured the retail world for days to found a good quality, padded, but otherwise snug fitting case for airline carry on, but a case designed for this unit would be better.This instrument is an excellent value.