nothing inherently wrong with the 350x.
it can't do bigger bits, though the 500x can use the bigger chuck and go up to 3/4" the 350x can't. Out of the box the 500x and 350x both go up to 1/2" bits. The part to 'set up' in the side of the 500x & 750x is better than using the grit wheel to align it.
Keep in mind all models only sharpen the tip, not the leading edge. I have a 750x so I didn't have to buy extra parts to make it do everything they can do. I did pick up an extra chuck and some wheels thanks for the promo code. I didn't even know they made a left handed chuck, that'll be interesting.