Dee,
Umm I was going to keep this quiet but Eliza has been in a portacot for 3 months now, she was getting her skinny enough legs caught in the bars and fat enough not to be able to get them out. One night she had almost dislocated her knee!!. So she sleeps in the port a cot until I am convienced she will be able to go into a bed. Great thing is it lower and she cant climb out another issue with her very expensive cot that sits and houses the stuffed toys now!! lol.
I think they are fine, there is no higher risk they may be a bit harder but go to Clarke Rubber and get them to cut some thick foam for the bottom and place a fitted sheet over it my girl she is tough and likes to sleep on hard surfaces like floors and has no problems in the port a cot.
Bec