Cheap and works, 'nough said. I personally dislike them because of their pitch, but then again everyone down here runs alert, so they peak out on the high side. In my experience lower pitched sirens like the Vortex, 28/2910, or 16V1T-B eat them from a far in terms of loudness except when the 2001s run in attack or happen to peak lower. I also dislike when they replace something that is legitimately louder or runs lower pitched like a P-15 or larger Sentry siren. I would go as far as to say that even with the 2001-130 being an "applicable" replacement for a Thunderbolt, a 1000 running in the 500 Hz range probably would outrun the 130 even with the 3 dB difference; the Equinox comes close to a 130 on paper with a 4-5 dB difference and about a 100-400 feet difference in range.
You could also take it from the Sentry or St. Louis County, MO perspective and side with omnis because of the rotators. While there is no omnidirectional siren out there that could match a P-50 or T-132, 16Vs and 28/2910s can be heard a mile away easy. When our city replaced Thunderbolt AT1000s and, while I greatly disapprove of it due to the money wasted, 2nd gen. 2001-SRNs they were able to obtain the same coverage in areas where the sirens they installed were WPS-2810s. Similarly Stewart County, GA ended up replacing their Vortexes with 16V1T-Bs and were able to get the same coverage. While I have nothing against rotating sirens and in some cases prefer them over omnis I can see the advantages of the omnidirectional sirens' ability to keep consistent 360 degree coverage of up to a mile, especially when it comes to Whelen's voice capable sirens... I mean by the time a 4004 or 3016 finishes talking the tornado probably took your house and the siren array right with it.
I get on them because of pitch. Companies want to make them put out an effective tone, but to most people the higher pitch may work better. I think that people outside this community will probably recognize the sound of a 2001, or any other 12 port or similar sounding electronic siren, faster. It seems that most media like to use the sound of a 2001 or STH-10 in their content when describing anything siren related. I think that our own WTVM used my recording of one of Phenix City's sirens with the picture of an Allertor at one point in a report when our EMA set the sirens off without any warning in affect... also the same day they started posting the parameters of what a Thunderstorm warning is on their site. lol "Is the city crying wolf?" *meanwhile 75 MPH winds take down trees and throw branches into houses* People can easily distinguish it from the environment, although some of the sirens that peak well over 800 Hz may end up making people confuse it for a fire truck siren. Of course if your from this area then the sound of a 435 or 560 Hz Whelen is what you'd think of, but there are so many 2001s, Model 5s, STH-10s, etc. out there that it seems like the sound of a 12 port siren is almost the norm.