While they look good in advertisements, the varmint lights are a waste of money in my opinion.
I tried some of them and wouldn't recommend a unit that mounts on the scope or rifle because you need to move it around to search for eyes with it and that's a safety issue for me.
Most times you need to shoot quick and that may end up with you shooting something you didn't intend to kill.
In the early days when I hunted mostly solo, I settled for a spotlight unit and had it mounted to a tripod with a swivel head.
It was a lesson in frustration.
I later graduated to a night scope after being educated in Night vision and seeing it's improvement on my kill rate.
Now I have digital and thermal scopes + viewers. Nothing is safe.
With the availability of cheap digital and traditional night vision around these days, I'm surprised the varmint light manufacturers are still in business.

If a $30 dollar light is all you can afford now, it's better than nothing.
If you can afford a decent night scope+ illuminator, do it, especially a digital scope that you can use during the day without worry of accidentally blowing the tube.