Star Hunter

Hello! I apologize in advance for raising such an old topic, but it is relevant for me. I am the owner of the Levenhuk Ra 66\400 ED telescope, it is an analogue of Sky-Watcher Equinox 66 ED or Long Perng S400M-C. I tried to connect it with reducer-flattener WO 0.8x II, but neither with the DSLR camera and with the astronomical camera I was able to get the correct working distance - stars at corners are blurry (field curvature). Searches led me to the this device - K1.0X-BU (FFL500-A02) Field Flattener As it turned out, it is produced under different brands (Omegon, Sky-Watcher, Orion), but I still could not find the test results with a 66 mm f/6 telescope. I am in doubt whether to buy it for my telescope or not.