ErgoPlay Adhesive Suction Cup Protector Strip, 2.25" x 3.75"

This film is a low-tack adhesive (not static cling, as a previous reviewer claims), and is initially easily removable; however the bond gets stronger with time (overnight), on both polyurethane and french polish finishes, and then feels like it could damage the finish upon removal. The adhesive is sticky and gummy, and feels like it could transfer to the guitar.
If you want something permanently low-tack and easily removable for your suction cups or grip pads, I recommend using the screen protection film that comes on new phones and tablets. I've been using some from a TCL Nxtpaper tablet (great for music) for several years, and it still peels off very easily and hasn't damaged either a french polish or polyurethane finish (I leave it on). A close second is a film from an old HTC phone. These materials are far superior to the vinyl cling films I have tried, which do not reliably stay on, and don't even stick to some of my french polished guitars. You should add a smoother tape on top for better suction cup retention (the films are textured), and you can glue on some rubber anti-slip for the sides as well, if you need a grip pad.
If you did not save your film, a decent second choice screen protection film is available from McMaster-Carr, item #1759N14. It's a bit higher tack, and thinner than the tablet/phone film, but after 6 months it still peels off easily, does not leave a residue or stain, and suction cups stick great as is. On polyurethane, I would maybe add a thicker film on top, as I have noticed a faint impression of the suction cups on one guitar after leaving them on the unprotected finish for several weeks.

Perfect

If you use an ErgoPlay or a SageWork support for your classical guitar, then these ErgoPlay Adhesive Suction Cup Protector Strips are a must-have for your guitar. If you use an ErgoPlay support that uses suction cups, you can use a damp sponge to wet the inside of the suction cups and form a tight seal on the protector strip surface on the guitar. If you use a SageWork support that uses magnets, then you don't have to worry about the magnetized connection leaving marks or wearing the down the finish of your guitar.

Made a mistake and fixed it immediately. I couldn't have been happier with the result. Good job, Matt

Works well. Have on two separate guitars