Socrates, in Australia, CMC (used to be D4F) have developed a bad reputation, it seems. A lot of news on our forums is negative regarding them. It has been claimed by some that artificial price spiking has occurred, essentially taking out hundreds of automated Stop Loss Orders, and in the process generating a bonanza opportunity for "someone" to buy in at a heavily discounted price, at the bottom of the pile of fallen dominos.
Apparently when CMC was asked about the spike, the position was restored, and fees refunded, because the "spike" did not occur in the underlying. This is because CMC is not a CFD provider, but a Market Maker - essentially a Bookmaker, who may charge the prices they like, if there are takers.
When deciding whether you should have your account with company A or company B, it has to be considered whether the company is a bona fide CFD Provider, or simply a Market Maker. There is a huge difference, and some have lost their accounts without learning the difference yet.
With a CFD Provider, you should get a GUARANTEE of the price EXACTLY matching the underlying, NO SLIPPAGE. For this, you have to expect to pay a commission. Many traders (punters) don't like commissions, so elect to have accounts with Market Makers (Bookmakers). They do not often get charged the fees up front, but these MM's are not charities - the money still has to come from somewhere. Unfortunately the mugs who pay the spreads, slippages etc are the ones who pay for the MM's yachts.
It's OK if you know what you are doing, and trade according to the risks. If a share is not very liquid (and there are still mugs who trade these, when there are literally thousands of other choices available), you can expect the spread to be wider. Why? because the MM often hedges by buying the underlying as insurance, or put options ditto.
CFD Providers almost ALWAYS buy the underlying instrument. You deposit a margin to cover a % of price movement, but they put up the lot. You may be asked to increase your margin (margin call), if the underlying goes against you. I am sure you are already aware of much of what I have said, but some readers may not.
I apologise if I have any facts askew, and will gracefully accept any chastening.
For me, it's NO Market Makers. If I could not be sure my CFD Provider was actually purchasing the underlying, I would not trade.
hth