Not bad, actually. And has optional space for two or three (if you move it one cell lower) coolant cells, allowing to connect reactor with redwire and/or pipes for automatic uranium reloading.
This setup can be used as mobile power source for miners, teleporters, etc.
I was screwing around to see if I could get 80 EU/t out of you little reactor. I couldn't, so I added chambers and water and got a Mark I-O with 80 EU/t http://www.talonfiremage.pwp.blueyonder.co.uk/reactorplanner…gjvkb9ms0659ukg
More screwing around gave the already powerful reactor a cheaper, internal cooling system: http://www.talonfiremage.pwp.blueyonder.co.uk/reactorplanner…xg5f4kwv3oe41s0
Not bad, considering the wiki states that there is a mathematical cap of 70 EU/t for Mark I units.
I think you missed the point of this thread Zulu, it was about "How to build a reactor with least possible components". 
Not bad. A little tinkering and I came up with this variant. It requires a bit more resources, but requires no water. It is a Mk II-1 reactor, but you can still run a full cycle before you need to let it cool down, so at least it won't melt down on its own.
Since it requires no water, you can literally build it anywhere.
It can get even cheaper:
http://www.talonfiremage.pwp.blueyonder.co.uk/reactorplanner…1501521s1r11r10
with the least possible amount of components to carry around
