I personally know the designer, developer and manufacturer of the GRIPPOD. Mr. Josesh Gaddini, formerly a Knights Armament engineer and previous owner of SWR Mfg. (Southeastern Weaponry Research) They develope and manufacurer some of the best sound suppressors available in the suppressor market. Im my professional opinion they are second only to Barry Dueck's Surefire suppressors.
Vertical foregrips ? I've used them since the first grip was introduced by Knights Armament for the SOPMOD block I program. Personally I found them to be useful, especially for taping a tape switch from your light or laser module for constant on or momentary illumination and IR laser use. In those day's we used a piece of bicycle inner tube to strap the tape switch onto the side of the Knights foregrip. It wasn't the best, but it worked.
Tango Down foregrips are pretty much the standard in this day and age. They are designed well, very rugged and now come with a American Defense Manufacturing throw lever for quick "on and off" placement of the grip. They are also now designed with a groove for the Surefire and other tape switches. The groove is made to hold the tape switch into place without the need for ties or rubber bands. The end cap when screwed back on provides a lock on the bottom of the tape switch so it never comes out or loose from the foregrip.
I still currently use vertical foregrips, but as a handstop, not an actual grip. Yes, other handstops are available from Knights Arm and Magpul with their Angled foreward grip. Either way, I want them on my rifles. The GRIPPOD is currently in use with many of the SOF community and Marines. They do serve their purpose and provide a stable platform from which to shoot from when going from standing to the prone shooting position. Some people like them, some do not. It's personal preference.
Just my experience.