Not a fan of SPAV, in part for the same reasons I'm not a fan of STAR:

1. It doesn't eliminate strategic voting. For example, imagine you support two candidates for a multi-seat election. Under straight AV you vote for both of them because there's literally no incentive to do otherwise. Under SPAV, you might decide that since one of those candidates is much more popular and thus a foregone conclusion to win that you should avoid voting for them so the value of your vote for the other isn't reduced. Too many doing this can cause negative effects, like strategic voting in other methods.
2. You can't tell me how my vote will actually be counted until every other vote is counted, because how the ballot will be measured in the end depends on every other ballot as depending on how everyone else voted your votes for some candidates may be worth less than your votes for other candidates. Straight AV doesn't have this problem, your vote is exactly what is says on the ballot and is counted exactly as it is on the ballot. The extra math also makes it more complicated to explain to voters en masse, which is a problem with other systems that have transferable votes.

I get that the goal is apparently to make every state elect a split legislature/congressmen by making so that if any seats are even vaguely competitive the parties will essentially be forced to take turns.