I recently purchased the VIFLY ShortSaver 2 Smoke Stopper, to use with my Speedybee Bee25, which uses 4s batteries.
Because the power input plug (XT30) is fixed to the body of the frame and that fact the cable from the battery is only 50-60mm in length, it’s impossible to fit the spark stopper when the battery is mounted in the frame.
The battery mount on the Bee25 can be rotated through 90 degrees, so that larger (dimensions) batteries can used.
Oh… if you want more proof that you don’t need/want a spark stopper (you do want a smoke stopper)… then this video goes on and on and on in more detail than you’ll ever need about what they do… etc…