Anybody using Market on Close orders to avoid bid ask spread?

[Igi]

I am wondering whether I can avoid both a: the spread on Market Orders, and b: the risks of Limit Orders, by using "Market on Close" DMA orders.

In particular, am I right to think that ...

A. Buying (with the intention of selling) using a Market Order, incurs an immediate loss of book value equal to the spread.        ... Alternatively ...

B. Buying on Limit Order, subjects me to the risk that if, while the order is on the order book ...

1. there is bad news, then my order is likely to be taken off the order book at my limit price, leaving me with a loss; or
2. there is good news, then the market is likely to go up and my order is likely to remain unfilled, loosing me the potential profit.

As I understand them, both "Market on Close" buy and sell orders go through at the same closing price. Thus there is no spread, and any risks should be balanced.

However, something in the above can't be right. I understand that IG's DMA needs a bit of setting up. Even then a few LSE shares still do not have closing or other auctions. Also, sSome people want to trade urgently, rather than at the market open, mid, or closing times. However, I don't understand why everybody else is doing this, and therefore thought I should check here before trying it.