Well the set of LaBella Low Tension Flats I ordered arrived today. I've put them on my Steve Harris P and what can I say, an absolute revelation!
The only time I'd tried flats previously was when I'd bought a bass where they were already fitted, or at a jam night etc. I'd liken my previous experiences to trying to play coat-hanger wire.
These however feel and sound superb and the tension is fine for me (I do like pretty light strings). I'm really loving the sound. Embarrassingly it's like a penny has dropped and I've finally realised what all the fuss is about with flats. It's the P sound and I'd not really appreciated the almost fretless mwahh quality you get, plus the difference in sound when really digging in.
I'm very pleased with them and they'll certainly be staying in place. May even try a set on the Stingray too.