I purchased the Flip-Flat for my FSQ-106 and like it a lot. It’s well-made, and it's a necessary for my camera images, thou I found the included plastic strap for mounting is a bit loose, I can replaced it with a large metal “hose clamp.” if necessary. Using with SGP for automation while I sleep, it’s very handy that it will record flats and close to cover the scope at the end of the night. As others have said, I don’t trust it for bias or darks in daylight, because it seems light will leak in, so I simply record those with the camera unmounted and capped during the night.
This equipment can be a bit over prices I disagree that it is a luxury item... any more than filters, reducers/correctors or PixInsight.
Good quality flats are a requirement and anything that makes taking good flats consistent and reliable is worth every penny. Look at the hundreds of posts on CN about problems processing lights with flats, the majority of which have to do with the quality of the flats in the first place. High quality, astro-dedicated like the Flip Flat eliminate that problem. iPads, cheap LED panels from Amazon and the like are NOT valid substitutes.