While the NTS-1 is indeed limited due to its monophonic nature, the amount of features this little beast has is amazing! The oscillators are what you expect from the Monologue's engine, the filters are really fun to play around with, and the on-board effects just make the whole thing sound even better! That + all the other features such as ADSR, LFO, Aux in and so on just make this synth so worth it for the price. Definitely recommend it!
NOTE: While it is possible to apply the FX of the NTS-1 to external sounds, it is not possible to use it as a "send" module - meaning, whatever audio you will input and process through it, it will always export the Dry + Wet signals (at least to my knowledge!). This means, if you're using the NTS-1 as an aux effect on a mixer, you will get the dry signal from the mixer, the wet signal AND the dry signal again from the NTS-1, so beware!