They do get easier to use and seem to be all fairly similar. Some have wheels and some have a bassinet insert for using with small bubs. Angus sleeps in his several times a week as we spend a fair bit of time with his cousins and sleeps as well as in his cot. You need to be careful about putting extra mattresses in on top as they are not designed for this. The greatest safety issue with portacots is babies getting stuck between an added mattress and the side.

From Choice:
Don't use a portable cot if your child weighs more than 15kg.
Don't put additional mattresses in the cot.
Inside surfaces should be free of bumps, ledges and protruding parts so children can’t hit their heads, get their clothing snagged or use them as a foothold to climb out of the cot.
Look for possible entrapment areas, where children can trap limbs, heads or fingers.
There should be no sharp edges or points where a child could injure itself.
The mattress should be firm enough and fit snugly without gaps on any side.
Remove all toys from the cot when the child is sleeping.
The rails should have two locking mechanisms to prevent accidental collapse and closure. Check these before placing your child in the cot.
The cot floor shouldn’t sag. Press down on the base to check this.