I'd say no, I'd avoid anything labelled as a bonsai in a garden centre and instead look at their trees/shrubs.
Cotoneasters are in every garden centre and can be picked up for about £8, fuji cherries are also great little trees (albeit it very slow growing), hornbeam hedging is another good option. You'll likely spend more than the £30 the privets cost but end up with better potential.
When I was first starting out I tried to get my hands on as much cheap material as possible - this included ebay bare-rooted trees such as japanese larch and again, hornbeam.
All depends on how much you want to spend, how dirty you want your hands to get, how much space you've got and how much time you want to wait.