Scotland is split pretty badly. Those who were cast on the scrap heap during the Thatcher years will never vote Conservative until the day they die. But they are so incandescently angry with Labour they won't vote for them either. Labour, in Scotland, has been unable to separate the "elite English" label from their Scottish heritage and voters are dead set against them.
Then there are the core SNP voters. They want independence and they don't care what it takes to get it. So they vote SNP.
The main thing to try and work out is how many disaffected Labour voters the Alba party will pick up, taking from the SNP and how many will stick with the SNP no matter what. I suspect those who stick will be core Nationalists.
Referendum votes aside, you can pretty much gauge the support by how well SNP does. They have not made over 50% of the vote since the failed referendum, so that vote for independence is not there. In that case, those who vote SNP as a viable option to the other non viable parties, may choose to vote Alba.
Whatever happens, it's going to be interesting.
Also useful to remember that Scottish elections are hybrid PR. Alba will be going for the list. If you know Scottish elections you know that they will get seats and Salmond will get a position back in the parliament.
That should be extremely awkward for Sturgeon.