Worth it? That's a completely subjective value judgement. I will say that the Kleemann numbers look very believable. But worth it? Maybe not.
I'll explain. I just had my 2006 SLK55 tuned by EuroCharged last week. Obviously a different engine with a different starting point. But identical displacement.
Peak Power (bhp) Stock= 355 Eurocharged= 379 or 6.7% gain
Peak Torque (lb-ft) Stock= 376 Eurocharged= 402 or 6.9% gain
The peak gains are about 7% for both power and torque. But.....the entire curve is lifted across almost the whole operating range of the engine. See graph below. So, you can feel it more than a 7% peak gain might imply. But it's mainly the torque increase you "feel", especially in the low to mid-range.
The cost? Jerry honored his March promotional pricing of $399 for me as I've had other cars tuned by EuroCharged and I already own their OBDII cable. I like the outcome. Yes, I can "feel" the torque increase and the throttle remap. The car is more fun to drive.
Now for Kleeman and your R172.
Peak Power (bhp) Stock= 415 Kleemann= 440 or 6.0% gain
Peak Torque (lb-ft) Stock= 398 Kleemann= 415 or 4.3% gain
The gains are lower on a % basis so it would indicate your engine is better tuned from the factory. Tuners aren't able to get much more out of it. Not surprising as the factory is trying to get more out of its next generation already. The interesting thing is that Kleemann wasn't able to get the same sort of gains on torque. And that's what you really "feel" in your butt dyno. Also, Kleemann does not publish a graph of the entire operating range so it's impossible to tell if that peak gain is in a narrow range or across most of the useful power band of the engine.
Also, both EuroCharged and Kleeman remap the throttle response as part of their tuning process. This is the second modification that you will "feel". Eurocharged did a great job with the M113 E55 engine in my car. The car feels more like a clutched setup and less like a torque converter because of the more direct throttle response but with no twitchy behavior like leaping off the line or unwanted wheelspin. I assume Kleeman may have done something similar with the R172 engine. But again, whether you can feel it depends upon how the factory tuned your car to begin with.
Lastly, the Kleemann tune is $1,530 (US) at current exchange rates. That's pricey for the gains they offer. Only you can decide if it's "worth it". Personally, I'd want to see a graph of the gains over the entire power band before deciding.
Good luck whatever you decide.