We have never sold a Shetland breeding tup yet, and never would even try, so I agree with that. I doubt it was Bloomer's reason for leaving them intact.
We have never found intact male Hebs or Shetlands to be difficult to manage. The only wee devils I wouldn't trust out of my sight is Soay, who are 'very keen to work'. Yes, if you haven't enough paddocks to keep entire males at least a couple of hedges or fences away from the females, there's all sorts of shenanigans they'll get up to, even without jumping a fence. But with good management they're fine, and as Porterlauren says, entire tups finish better than wethers.