Ok the one you were using is nothing more than a spike suppressor, and yes spike supression does wear out over time and multiple "Hits"
The one you have now (the 34850) not only offers spike suppression, which by the way can be easily renewed. but high/low voltage suppression, time in (Which is an additional form of protection) and more It is the model I have as well.
Spikes are short (Usually less than 1/60 second) rises in the voltage.
But low voltage is often more damaging. trying to start an A/C at say 100 volts, can damage the motors big time at 1,000 to replace.
Likeise folks have been known to plug into an 240 volt outlet (30 amp) thinking it was a 120 volt. ... again the unit you now have with the LCD dislay will protect you (The older one would not) and inform you. This too can easily cost thousands if you do not have protection... Short story at end.
Finally the "Time in".. I have been through several power failures. when power fails and is restored.. Many A/C's and other heavy loads kick in.. Well the power line voltage goes on one heck of a rollar coaster ride. again this is damaging.. Lasts, generally less than a minuite. but since it takes nearly 3 minutes for your new surge guard to pass power.. YOU ARE PROTECTED,
This is a very well built unit. works well but .. Only a 1 year warranty
The PI units are also very well built. Work well, and come with a lifetime warranty.