Alternates would be:
 
http://www.ikmultimedia.com/products/trquadimage/
 
http://www.toneprojects.com/products/plug-ins/basslane/
 

WARNING!! I just bought this and threw it on the master bus of a couple songs to try it out. I hit the stereo/mono button on the master bus to check it in mono. Immediately this caused a feedback loop and the volume quickly was getting out of control. Bypassing Mongoose eliminated the problem. I barely had the width over 100%. So warning to anyone who has Mongoose. Turn it off if you're going to check your mix in mono.

Leadfoot
WARNING!! I just bought this and threw it on the master bus of a couple songs to try it out. I hit the stereo/mono button on the master bus to check it in mono. Immediately this caused a feedback loop and the volume quickly was getting out of control. Bypassing Mongoose eliminated the problem. I barely had the width over 100%. So warning to anyone who has Mongoose. Turn it off if you're going to check your mix in mono.

Might be worth reporting it to them...

Leadfoot
WARNING!! I just bought this and threw it on the master bus of a couple songs to try it out. I hit the stereo/mono button on the master bus to check it in mono. Immediately this caused a feedback loop and the volume quickly was getting out of control. Bypassing Mongoose eliminated the problem. I barely had the width over 100%. So warning to anyone who has Mongoose. Turn it off if you're going to check your mix in mono.

VST3, VST2 or both?

I only installed VST3.

I got this free. It's a nice tool to have in the box. There was a free beta version and those of us who got it, Got the final version free. Good deal.

Can anyone reproduce the feedback loop issue when switching to mono?

Also using the vst3 as the last processor on the Master bus and can't reproduce it. This was one of the first things I tried after installing just to ensure things weren't collapsing (much) when I switched the Master bus to mono.  I have tried it several times while the project is playing. I'm using the default mongoose setting with the exception of having the xover set around 380Hz. vs. 400Hz.

Leadfoot
I only installed VST3.

Do you have the 64bit Double Precision Engine enabled in Preferences > Audio > Driver Settings? If so, try turning it off.

scook

Leadfoot
I only installed VST3.

Do you have the 64bit Double Precision Engine enabled in Preferences > Audio > Driver Settings? If so, try turning it off.

Good observation scook!
I just checked mine and I do Not have the 64bit Double Precision Engine enabled. Perhaps that might help Leadfoot.