Sure, it's lacking from the real thing, but at least you keep your mind going and don't hit the same club 20 straight times. If money is a problem, there is no cost to use a putting green at just about any club. In addition, practicing your putting is the fastest way to improve your scores on the course. If you take two putts per green, that's 36 shots on the greens alone. The same goes for chipping.
Most amateurs miss three out of every four greens during a round.
Keeping sharp the feel and touch that you develop around the green is key to scoring well. If money is not a big problem, but time is, consider getting lessons. There is a multitude of teaching professionals. You and your friends could approach a professional about a group lesson and save a few dollars. Getting lessons in this way relieves you of the worry of embarrassing yourself in front of strangers and your entire foursome stands to gain a little improvement.