The comparison is natural, both are 4 seater, both have gull wing doors. One cost double the other.Any design needs to account for potential problems. The gull wing design allows for good exit in case of an inverted crash situation. The CH-640 has a pillar support to help maintain canopy shape if inverted.
The main complaint about the CH-640 is the back seat. Its not big.
Most people judge the CH-640 on the factory prototype, the plans have been updated since then and the backseat has been moved back and a lower floor modification is available to add inches there also. Below is a video reflecting some of these changes over the factory prototype.
Watching this video, the back seat passengers look like they are having a good time in this CH-640.