It's manual says "The EP-09 is the first electronic piano with a built in micro-computer". They're referring to the arpeggiator. The manual goes on and on about how great it's arpeggiator is. It's not as good as the arpeggiators on the Juno 6 and 60; and it's virtually useless because there's no way to control it externally.
The EP-09 is extremely limited. I'm sure it pales in comparison to the EP-30 (the first velocity sensitive electric piano released by Roland in 1974) and the Roland EP-6060 looks much more versatile. I was originally drawn to it simply to complete my 09 family (along side the SH-09 and RS-09). There is something very special about all the 09's and the EP is no exception. It has four different sounds, the manual describes them as:
I...soft piano tone
II...hard piano tone
I...orthodox harpsichord tone
II...a bright harpsichord tone
These sounds can be mixed with one another in any combination to achieve varying degrees of brightness or dullness. In my opinion it sounds remarkable. I would describe it as a crystal clear tone, it's a tone that I would normally associate with the Juno series, but here we have it from an analog machine. It is polyphonic, I suppose I should mention that and speaking of polyphony: I also think the sound of the RS-09 (Organ and Strings) can be reminiscent of a Juno but the lack of decay and sustain controls make the short, punchy piano sounds of the EP-09 impossible to obtain. The EP-09 also lacks decay and sustain controls (it's "sustain" feature works more like release if you ask me), so of course the lush pad sounds of the RS-09 are out of the question. Each family member serves it's function in the house of 09.
So, while it is incredibly limited, if you love the sound you'll be delighted by the EP-09. There is something very nostalgic about it. I'm not saying it's used in this song, or any of the sounds in this song sound anything like it, but it always reminds me of this sing in spirit and I think the EP-09 would have fit very nicely into this song: