Highlighted in red on the far left is where they mention the sirens.
2016:

2017:

2018:

2019:

2020:

The main replacements seem to be centered around the older Whelens, as they are slowly but surely starting to show their age. Several along the Branson strip have had failures recently, and several had major issues during a recent tornado warning in March.
Here's a few videos of sirens from their system:
SD-10:
https://www.youtube.com/watch?v=CZVSSCh6Ueg
2750 (Has since been moved to replace an SD-10 that got hit by lightning a few years ago, 2907 was installed a few blocks away)
https://www.youtube.com/watch?v=5L_Al7LbYtw
Tornado Warning ambience:
https://www.youtube.com/watch?v=TX1UzOa393Y