Airflow is similar. Tengu build is straightforward, two post build although the distance between them is tight even for a 2.5mm coil. The Merk is a matter of taste and practice although I still find it a bit
cramped but its difficult to explain as it is an odd deck design. The main issue for me with the Merk is the JC. I have struggled with juice flow for a while but eventually realised that, at least with build I currently have in there, I need to open the JF but maybe 4 full turns. Not sure how that fits with the experiences of others. Taste-wise I would say the Tengu is superior but, even if you can find one (try the classies here if you havent already seen it), its more expensive. Given there are so few of them around, be prepared to pay pretty much RRP or even more for a used device! Anyways,I like them both but if I had to get rid of one, Id probs sacrifice the Merk (and then buy it again later lol!)
One important thing with the Tengu is that of course, Tark is not making any more. That means that spares will be impossible to get hold of. I am think specifically of the posts, and the whole +ve post assembly all of which are different degrees of fragile. If you get one, be very careful when you disassemble the base for cleaning! In contrast, the Merkava, as befits its name, is built like a tank...