The Arranger keyboard developed from the Electronic Organ (Electone) and is essentially a single keyboard version, compared to your EL 25 however, things have moved on since this was produced, both in Arrangers and Organs (Electones) and so you now get more of everything that you were used to with your EL 25.
Point to note is that most people that have changed over to Arranger keyboards from Organ (Electone) usually add a Pedal board after a short time otherwise there left foot does not know what to do.
A Workstation is more a production/Group machine rather then OMB, although these days the differences are beginning to blur.
Hope this helps.

Bill