What's good about Meta-trader4?

I trade at present on a web based platform supplied by my broker. I've been told by my friends that MT4 is much better... but they're not technically knowlegeable enough to tell me why.

They vageuely mentioned something about slippage being a problem on web - based trading accounts because of the time delay after clicking the order close button. After you click the close order button it takes time to go to the broker and then be execued. By that time there has been some slippage.

I've been told that this does not happen with a computer - based trading account like MT4.

Can anyone advise further please.

What your friends told you is complete BS. While there might be some difference in how the 2 platforms go about placing the orders, the latency should be about the same, therefore you will not see much difference as far as slippage. So in that regard going with MT4 will not give you much in terms of an advantage. That in combination with the risk of going against the MT4's dealer plug-in, and MT4 looks worse in that regard. I use both, a java based platform (web) and MT4 and i can tell that execution is better/faster on the java platform. Of course that will somewhat depend on the particular broker...
Now as far as advantages of MT4. With it, you can develop/use custom indicators, which are abundant. Also you can create EAs which are essentially trading robots. Also there may be more drawing tools than some java based platforms will have. The best thing to do is get a demo account with a MT4 broker and try it out. Keeping in mind that execution will be different on demo than live and you should still be able to get a good feel for what MT4 is all about. HTH

And stop talking to your "friends" about trading. They don't know anymore than you and they're only going to fuck you up.