Yes, I have experience and plan to alarm each of my bikes. I don't fully agree that it won't make a scrote think twice. Yes, the scrote won't think twice in the attempt but the alarm itself should either deter him from continuing or be enough to alert me.
My main use is for security at a cafe stop. While we always keep the bikes in sight I know we're not actually watching them. The purpose of the alarm is to alert me to interference with the bike. Create enough time to get outside. I also set the alarm while the bike is in the garage.
The alarm linked below gives one gentle bleep when the bike is moved, this is really a reminder to me as the user. A second movement sets off an earsplitting alarm. It is very sensitive to movement. I've ridden with mine in all weathers.
My buddy was able to unlock a digital cafe lock without setting it off but he knew the bike was alarmed and it took him a couple of minutes of very careful movement. If he'd then picked the bike up the alarm would have sounded.
It's an ugly beast but can be hidden under the seat, in a bag etc. I think it's worth £15 to see if it works for you.
Cruxer Bike Alarm with Mount,USB Rechargeable Wireless Anti-Theft Vibration Alarm,110db Volume and Sensitivity Adjustable Sensor Burglar System with Remote for Motorcycle Mobility Scooter Caravan: Amazon.co.uk: Automotive
https://share.google/P8Curke7VSNra9R9u