The Cullmann Nanomax 200T (not sure wether this is the "52001") is solid stable without extendend legs, even more if you take the "spreaded" position. only problem: the grass might block your view
One extension is a bit criticial for balance, the height/base surface ratio is not that optimal, but in the field I normally find a suitable spot to have one leg spreaded. so if you are NOT on a flat field, there is always a stable position. Im quite creative in positioning it
Fully extendend, i would not mount the sigma 150mm with camera on it, it may hold, but i couldnt be at rest nearby, even more if there is more than the slightest breeze
The head should be replaceable - never tried it as a havent seen any lighter head, and a ballhead is ok for me; its the weight that counts
I have tested it for travelling - walked with it all over the Zwischbergenpass (~3300 meters over sealevel), thats some 1700m ascent in two days - took the 600D, 11-16 tokina, 40STM, 85f/1.8 and sigma 150mm OS and of course this tripod with me - and some other things like food and clothes
It was the weight of the sigma that nearly killed me...