Recently got a big box full of vintage tools and electrical stuffs. I came across this strange looking (seems vintage by its looks) button device. Its the first time I came across it.I googled and read that it can be of two types thermistor and diode type. The later actually uses one half of cycle to increase filament life.
Your diode type bulb saver is just a halfwave rectifier .It will not be good on a CFL .Half wave rectifiers like this draw DC current of the AC mains and lots of harmonics of even and odd order .The power Authoraties in most countries will not permit this these days .Do keep your antiques because they represent a bygone era and the NTC thermistor ones could be useful because they do reduce inrush current .