The best thing about a private pension is the tax relief. That is as good as it gets!
The main pitfall is the charges levied by the industry. Most pension funds grew by just 4% over the last 30 years but the average fees are 2%-3%. So over half the gain is being swallowed up and lost by charges.
80% of private sector workers have less than £30,000 in their pension pot. Around 90% of all private sector workers would be better off NOT saving in a pension at all as they would then get pension credits and other means-tested benefits.