We bought a refurbished U3 for under 3.3K about 3 years ago and got 18 month interest free finance. So financially there wasn’t too much burden.
We had no knowledge or experience on pianos with no musical background. We basically just walked in to the local dealer’s store looking for a cheap piano for our daughter who had not even started learning piano yet. But after serval trails across the board, we could notice the difference between good and average pianos without knowing their prices. We also tried U1 and U3 but we prefer the richer sound of U3. After hearing the difference there was no way for us to go back to cheaper ones so we just bought the U3. Based on your thread, we should have been very lucky to have access to both U1 and U3 at that time?
It proves to be not a waste of money. We are enjoying the sound of U3 everyday and my daughter is progressing slowly but steadily. She got Grade 1 distinction last year and recently won a local piano competition at Grade 2 level, where she got a chance to play on the dead expensive Steinway concert grand piano. She said there wasn’t too much difference in playing but the grand piano does give much more powerful sound and she liked that! But I did see some children was underperforming on the grand piano on the day.
She also performed on a digital piano at school recently and I could hardly notice any articulations from it. So I would not recommend anyone to buy a digital piano if taking it seriously, as even if the keys are weighted the sound it produces is still far from real. You need to be able to hear what you are playing before learning how to play!
Your child is already at Grade 3 level, and it won’t take him long to reach Grade 5. I would recommend you to invest as much as you can now! By the end of the day, you buy expensive, you sell expensive. There is nothing to loose.