I don't see the added benefit of pooling coins in a POS setting above doing it yourself in your wallet. Well, minus the work that it saves you.
The main benefit is the reduced orphan rate. A staking pool allows a bunch of people to cooperate, and effectively agree not to orphan each other's blocks.
Then there's the fact that most people don't keep a server online 24/7, and so a staking pool allows them to be always staking without having to maintain their own server.
There are lots of downsides of course, with the biggest being the counterparty risk and the fees you'll have to pay.
Proceed with extreme caution it appears to be a black box you put money into and a trickle of money comes out of because magic or staking or something. If you wish to withdraw principal you pay an unspecified penalty. Transparency about zero as far as i could find with limited digging.
I've not looked at their site, but there's no excuse for such a site not to offer a proof-of-solvency, so its clients can be sure they're not investing in a Ponzi.
I will have to do more research before considering any sizeable investment obviously, since its legitimacy cannot be confirmed as of yet. I have a smaller investment there in order to try it out, so I will see how it goes.
I am no crypto-expert, but in the thread there any reasonable arguments that suggest transparency and proof-of-solvency, while others claim the total opposite... The usual. And of course the owner could run off with all of the investments, but if the service is half as good as it claims to be, he won't have any reason to do that unless he is related to Scamtos.
The owner of Stakeminers explains the need for withdraw fees in the thread, and it makes sense. It is in place to prevent sudden mass-withdrawal that will damage the effectiveness of staking. Unless you have a need to withdraw your investment prematurely, I don't consider that a fee. You can withdraw all of your earnings for free. Apparently, people with smaller investments can get the premature-withdrawal-fee waived by asking, which I guess can be a good option for people who are sceptical, but who still want to try it out.