When I looked it up on yaesu, the first difference was the big colour display and the impression it was bigger than the FT-897D. But I was more interested to see the specifications, and here they are:
|Feature||FT-991||FT-897D with internal tuner and battery|
|Weight||9.5 lb (4.3 kg)||10.3 lb (4.7 kg)|
|Battery capacity||---||2200 mAh|
|Power consumption RX||1800-2200mA||600-1000mA|
|Impedance||16.7-150 ohms||4-800 ohms|
All in all, the conclusion is that the FT-991 seems to be a very nice radio, with a colour display, an USB port and new features, and is a welcome addition to the Yaesu line, but is designed with a different style in mind and is therefore not a direct replacement for my Yaesu FT-897D with internal tuner and battery.