Yes DSO feasibility is a pretty easy thing to assess. SL1 is a...

Yes DSO feasibility is a pretty easy thing to assess. SL1 is a good example. Another example is PLS who didn't do any feasibilities for DSO.

What do you need to know for a successful DSO operation? 

1. Can you sell it for more than it costs to dig it out of the ground? If we can prove up pipes at 2% that is basically the grade that Gabba twins are generating 1st step concentrate at so should sell for an ok price. Literally means a buyer just has to do second stage processing to get 98% V2O5. Let's say in the current market we can even sell it for 30% payability on contract prices. Let's say contract prices are $15/lb at the moment (not sure what they actually are). So we get 2,200 (lbs) x $15 (price) x 30% (payability) x 2% (grade) = 200/t. Cut that in half again to $100/t and you are getting roughly what Li DSO is going for. 
2. An ML/Environmental approvals. Obviously needed before an operation can start.
3. An Offtake - this is the key to the TNO DSO plan in my opinion. If they can find a buyer I see it as a definite goer.
4. Can we fund pre-production capital. Refer to point 3. Given pipes near surface cost should be low and offtake gives certainty.

Sorry @Chrissyw0w forgot to reply. I hold AVL and TNO much for the same reasons as people have given. I see AVL/TMT as solid investments and TNO as a bit of a wildcard that could have big potential. AVL/TMT probably sector leaders though. AIMO.