Jim Chung tested this new adapter
The MTF curves do appear to demonstrate that the Viltrox has the sharpest centers with a rapid falloff halfway across the frame but the undeniable take home message is that it is as good as the Metabones. For a whole lot less. In fact, the current eBay listing shows a price change already to $200 USD so demand appears to be healthy. I heartily recommend that this little trinket find its way to your favourite m43 user’s stocking.
And here is a Viltrox EF M2 vs Metabones Ultra 0.71x (with Sigma 18-35, Canon 50mm 1.4):