I had the opportunity to get these headphones through American Express reward points.
I took this new headphones because my "old" Microsoft Headphones were at the end of their life.
I used them a lot during the day, to listen music, make some calls and listening podcasts.
Thank you for your service. :)

First of all, the HD 450BT are cheaper than other Sennheiser models but they are good if you want to use them for traveling or as a remote workers for conference calls.
The active noise cancelling is good but not the best.
You can hear noises in the background but the quality is good (at least for this price).

What is very impressive is the battery life. I test them for few days and I always obtain more or less 26 to 28 hours (with music and ANC enabled).

You can connect two devices at the same time, but you can receive notifications only for one of them.

I don't like very much the design of the controls on the headphones.
There are a lot of mechanical buttons and it's not easy to remember which button you are pressing or switching.

There is no fast charging support and the headphones needs more or less 2 hours for a full charging.

Conclusion

I am pretty happy about this headphones.
Especially for the sound quality and the battery life.
I am not happy about the low quality of the case to bring them around and the buttons layout.

If you want a cheap headphones but with a good quality, buy this product :)