Bullshit.
I have a fast PC, I solved all the 48 puzzles, and WITHOUT setting them to "slow snakes" mode.
Use
BOTH mouse clicks
AND keyboard keystrokes if you struggle with some moves (first move with a device, second with the other device).
Note: By "fast PC", I mean that with a maximized window (not even "real" fullscreen), FullHD, the game never use more that 1% of CPU on my PC... There is a "peak" when playing fullscreen animations, at 5% CPU (less than 2% if window is at its native size). I think it's "fast enough"...