The main difference is in your first sentence line, the other projects are just like your regular cryptocurrency but this project is a stablecoin meaning the price of Gold token is totally dependant on the price of real Gold. Therefore if real good was to achieve an increase in price, It'll reflect on the gold token. The other projects you speak off, although they claim to be backed by gold, their prices is totally dependant on the trading activity of the community and their volatility nature is just like that of your regular cryptocurrency. That's why you can see their token price raising from cents to dollar values then fall back down when the hype surrounding the project is over or investors loses interest.
Irrespective of Gold token been a stablecoin it also has other advantage that the average stablecoin don't, it can be used as an investment vehicle since it's price is corresponding to that of the real gold meaning an increase in Gold automatically gives you profit in gold stablecoin. Concerning the credibility of the project, you can verify that on their website, audits page;