It was even more interesting before the latest hardfork when they decided that they don't need miners anymore and added a 1 year period for miners before their coins become available for use. The coins of course gain interest in that 1 year, but it essentially has driven away miners and pools and the interest in the coin has further decreased. They favor HODLers that buy coins and keep them to earn interest, unfortunately with the very high interest rate and miners going away, the future of this coin is quite uncertain... so do a careful research what you might be getting into.
1 year is the same as the average weighted form for obtaining STEEM from POWER. Only difference is that you obtain STEEM weekly, as opposed to all at once. This probably stabilizes the market more so than HODL'ing, but who knows. It's an interesting experiment. HODL was technically first to market for long-term deposits; even if the idea for POWER was independent (which I believe it is), there is no way to prove that (beyond maybe using a time-stamping blockchain based record for the idea of a private project which would require revealing your private key to prove authenticity of an encrypted message, assuming you don't want details of the entire project known prior to its release).
First to market almost always has an advantage.
You may find it similar to Steem Power, but the problem is that most miners don't like the idea of not having control of the coins they mine. Some mine and sell immediately to cover costs, some mine and keep coins for a period of time, some may hold them long term. All of them want to be able to control their coins. Steem Power gives you some value and has some functionality on the steemit platform as you hold it, apart from the interest rate that increases your holdings, but mining HODL and being forced to wait for a year and in the end you just get more coins.
The problem is that by the time you get control of your mined coins there will be a lot of coins available on the market and the market will most likely not be able to take them as they are driving away some of their users and are hardly attracting new ones. There needs to be some other use for the coin other than just holding it for the high interest rate and there isn't for the moment. Most mining pools also stopped, there is just one new one that has brought a very small portion of the miners back for a second try, but it is questionable if they will remain for long - http://hodl.optiminer.pl
Correct, there is no immediate usage for coins held in deposit. It'd be interesting if one could trade deposit accounts on an open exchange, even if they are still locked up.
Essentially they are closing up more in favor of their existing HODLers instead of opening up to a wider audience and attracting new users to the coin. I was actively following it before the hardfork, mining, trading and holding (short term), but after they changed the rules I just lost interest and I suspect a lot of other people also did.
Being able to trade long terms deposits would be interesting, however I think that this is more reasonable to be implemented on the local wallet than on exchanges. Hardly seeing a more complex feature implemented any time soon when they still have not added the option to sort the term deposits in the wallet for months... :)