I think the OP poster is referring to the Mio Anti-Glare filter like this one mentioned from this Ebay site where I bought my Mio 368 from. (Note I had to pay £41.83 import duties on top)
https://www.ebay.co.uk/itm/360788680015
You unscrew the front lens ring and then this anti glare filter screws on in it's place, I use it on my own mio 368, you can rotate the filter so it works similar to
a polarizing filter.
The Mio 388 accepts the very same filter, infact the 368 and 388 share the same camera body as they have a different mounting system compared to the cheaper 338 or 358 models, also the cheaper 338 and 358 models do not accept any filters as there is no thread on the lens housing.
Main difference between the 368 and 388 beside the fact that although the 388 is the older of the two it's also more expensive mainly because it has the GPS and ability to warn you about speed camera, with the right speedcams POI loaded.
The Mio368 probably has the slight edge on image quality as it also has WDR capability, but in reality I doubt there's actually very little difference between them picture quality wise. I've seen it mentioned that the earlier 358 had minor occasional blocking issues on some scenes when passing tree's ect, but I can't say I've seen any at all on the mio 368, image quality is not bad at all.
The main issue with Mio cams is just the very noticeable suctions mounts, otherwise well built, good reliable cameras. The motion detect is decent too for up to 1 hr, but at present with current firmware the motion detect which is rather good in that it also captures 5 secs prior to being triggered, meaning its continually recording 5 secs into a tiny buffer area, and retrieves it when it gets triggered so quite nice, it's just a shame it cannot be used while it's powered on, as the battery only lasts for just over an hour. A big failing!. Hopefully a future firmware update might resolve it, but I wouldn't count on it.
