There are no tests for these cots specifically in relation to cot death. However I believe if you have the baby within the confines of the cot, then it's counted as a separate sleep surface and therefore the same as a self-contained cot. Do follow the same guidelines - feet to foot, no unnecessary bedding or toys, etc. If you have them closer to you then it's the same risk as when co-sleeping.
You must be aware of the safety information provided with the products because when used incorrectly they can be dangerous. There was a very sad case a few years ago with the Bednest where a baby died. The design of the cot has been changed and warnings have been added but these weren't present at the time, it was simply that the cot was being used against the instructions - so it is important to be aware of potential hazards and recommended correct usage.
With DS I converted a cot as there wasn't much on the market. This time around, we have got a Waldin/Fabimax one from amazon. I think it looks fine and am pleased that it doesn't have a low weight limit like some of the more expensive ones, but I'm not sure about the space in terms of length. I don't really like the mattress but I can't find another to fit it. The ventilation is great so I'm not concerned about that.
IMO bedside cots are a useful "new" invention which is helpful in the context of co-sleeping, which isn't a new thing at all and has been done for as long as humans have lived, yet is associated with cot death particularly when risk factors are present. (modern bedding, smoking, soft surfaces etc) So actually bedside cots probably reduce cot death rather than contributing to it. Obviously, there are higher risks with a bedside cot than with a completely separate sleeping area but it does seem to be generally accepted that a bedside cot is one way of getting many of the benefits of co-sleeping while affording many of the safety benefits of a cot too.
Bedside cots will have to conform to British Safety Standards concerning cribs, cots and moses baskets, which are possible to look up.
Ultimately it's your choice to weigh up. If safety is your #1 concern then a separate, enclosed cot with no bedding is the safest thing, but many parents find that convenience and the baby's comfort plays into their decision as well - and your baby may not give you much of a choice about the matter!