It's a good deal if you think/feel yourself as a smaller club compared to the one making the deal with.
Another way to make the point:
This kind of deals with buy-back clauses happen between big club and smaller club for a reason.
Smaller club accepts inferior position compared to the big club, and essentially accepts that if the player is of the potential he is thought to be he would inevitably be playing sooner or later at a level higher than theirs. In that sense they prefigure a future sale to a big club by including the clause.
The logic of the exchange goes somewhat like that: We (big club) give you a temporary solution that - if it works - would improve you since the higher level potential would be materialized, and you i) give us priority in your future sale and we don't have to go into bidding war with other top clubs or accept unreasonable valuations, ii) develop the player for us. Of course, if it does not work (if the player is not of the potential he is thought to be), no one loses again, as the clause is never activated and the player stays at the lower level.
The development of the player is crucial in that deal. The work that the smaller club does is to verify that actually X player is of the highest potential, and it accepts that kind of 'outsourcing' for the big club for the single reason that they are at a lower level.
I cannot think of the top of my head any other such deal between clubs of same or similar caliber, because these deals always happen between big club and smaller club.
Now, one can argue that Spurs is not same level with RM. Historically that might be true, but currently it's dubious.
Mainly because Spurs play in the strongest by miles league, and even though they regressed a lot the last year, they were top5-6 in Europe recently.
So, Spurs will be developing a player for Madrid for two seasons in the strongest and most competitive league for 10 or 20 millions.
Edit: Even if they want to win now, and I accept that there might be truth to that, still...
It shows small club mentality.
Would UTD, City, Liverpool, Bayern and others accept such deal when they are in desperate need to win? Never...