Arranger keyboards generally come with 61 or 73 / 76 un-
All arranger keyboards will have a fairly large selection of pre-
Additionally, arranger keyboards have the ability to split the keyboard at certain (variable) points enabling different sounds to be played in each part of the board, (i.e. bass on the lower half / piano on the top half), and / or to use the lower half of the keyboard to trigger auto-
Most arranger keyboards have built in speakers, which are suitable for home use, but many also have the facility for adding external speakers for better quality and more volume. The most expensive models (Korg PA 4X / Yamaha Genos) tend not to have built in speakers as is the norm for professional equipment.
Most also have recording features, in some cases as many as 16 fully editable tracks enabling a fair degree of quality music production on the better models (Korg PA 700 onwards).
So who are they good for?
The lower priced models are ideal for anyone who wants to learn music in a fairly casual way and just have fun (for classical or jazz go for a digital piano). The more expensive models are ideal for solo gigging, or music production by more experienced musicians.