Monotrons should be in everyone musicians, or music/sound lover pocket. I'd say, too, that the price is quite much for what it does, in compare for what you can get for just little more money. It would be great to have it as optional gift for buying bigger Korg synths, but reality is, it's great pocket generator to not have it anyway. Maybe not for clean musical person, but if you really feel joy in generating, exploring and analyzing true analogue and dirty soundwaves, Monotrons can made it possible everywhere.
To other reviews, I'd add, there's little screwdriver button on backside, which changes LFO type, so from default triangle, you can get saw and from square you'll get different pulsewidth. With saw, you can easily emulate techno-drum and play with it.
Also, ribbon touchboard (also on Duo) is programmed in way, that if you press two points, sound generates note in between. It's little help in quite random tone finding of Delay's ribbon wide continuous scale, but it's something.
Also recently, I put Volca Sample into Delay and had very adventurous two hour train jam.