Seems too good to be true to have one board for both, but for a learning beginner is it actually reasonable?

Inflatables are fine as long as you get one with a dagger board fin which wll stop you from drifting sideways .

For sure.
Just got home from a week at Lake Cootharaba. Wind dropped to around 10 knots for the last 3 days. Spent all of this time only on my Starboard Astro Whopper.
Paddle in the early morning. Chucked a 5.0m on and had some fun in the light breeze. My wife who is at best sails once or twice a year took it for a few runs out and back. My 8 year old son and I went cruising on it together a few times as well.
Best of all I got to sail it behind him for the first time while he was on his/my Kode and 1.5 ezzy. Normally I am wading behind yelling advice/encouragement. Both very chuffed with that .
I take it in the small rollers at Cotton Tree with paddle and sail as well.
Honestly, would have to best the best value for money I have spent on sailing gear in the last few years, and it fits in the back of the car.