Wow, the Brinsea product range certainly is confusing! For example, the 'semi auto turning' models don't have a cradle - you have to rock them from side to side on their octagon shaped bits, which sounds distinctly manual to me!
The Octagon 20 range thus appears to be:
1a) Octagon Eco, with automatic temperature control, but a manual glass thermometer for checking it. No auto turn cradle - you just rock the whole thing back and forth on its octagon bits. No humidity measurement. Price roughly £125.
1b) Octagon Eco same as above, but with cradle, roughly £175
2a) Octagon Advance - Auto temp. control plus digital readout, plus control buttons to change the temperature. Humidity display in %. No turning cradle, Roughly £175
2b) Octagon Advance, with cradle, £200 ish.
3) Octagon Advance Ex - as 2a/b, but with water pump. P.O.A.
I do fancy having one with a humidity readout, so it looks as though option 2B could be the one to go for...... Decisions Decisions!