With mode S you become 'visible' on apps such as Flight Radar. Some may like this, some may not.
This is - sometimes - also true for the simple mode-S transponders that only sends alt/squawk/id.
This is because frlightradar uses a timestamp/triangulation network to get the position of the simple mode-s transponders. But it depends heavily on where you are, as at least 4 triangulation stations must be in view. Here in the copenhagen area it works from 2000 feet and up.
Check out the MLAT section here:
How it works - Flightradar24.com - Live flight tracker!