Do they actually stiffen up the front end like they say? What's the real benefit?

 

The idea is that under hard cornering the subframe flex's causing the suspension geometry of the lower control arms to alter causing poor dynamic alignment and worse traction. The flexing of the subframe is also going to absorb some of the load going through the car instead of the suspension.

Through bracing the lower control arm points and the subframe you theoreticly are preventing the flex by holding them in place.

However if you have ever removed the front subframe of a honda you will question how much force is really needed before that massive thing flex's. Your bushings will flex lightyears before.

So I wouldn't bother.

 

Awesome.