Those are the only ones that I have really had great success with. I have also used this one (https://www.amazon.com/gp/product/B07L6WHQ6H/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1) and it has worked fine but I had to use a few converters along with it and wouldn't really recommend it for that. I don't really have any great suggestions for features to look for. The extron converters are usually available on ebay, and I always buy them used as they are pretty old so I wouldn't even say the more expensive the better although that may be the case. I always use an upscaler after the panasonic output since the video quality drops running through the MX50 anyway.

Not sure that's at all helpful and it's a bit of a ramble but I don't have specific advice on other converters unfortunately.