It's actually a pretty good shot to use if you can do a forehand slice as hard as you can and land where you want it. Nobody will ever use it in professional tennis because the unforce error ratio is simply too high. Hit anything softer is just a dead giveaway
I don´t see why slice forehand would be any more vulnerable to unforced errors than slice backhand. Not many pros seem to use it nowadays, but I´m not quite sure why. Itś a good shot to have in your arsenal, if you use it correctly. Connors, for example, used to hit his forehand with some underspin when he had to hit it low, or from a difficult position.