Its not the same. ATF+4 is friction modified for smooth slip controlled shifts and TC lockup. So, it is similar to the SPIII which is just another HFM'd fluid.
As long as the fluid doesn't change the feel of the shift excessively, then it'll work.
If you decide to use a non-SPIII fluid, make sure that the torque converter locking and tranny shifting remain the same as before. If not, you should dose it with a fluid converter. Abrubt shifting and TC shudder means that you need more fluid convertor.
MerconV and multivehicle fluids are highly friction modified more so than Mercon/Dexron. But, they might not be HFM'd enough.
Enough HFM'd = smooth shifts and smooth TC lookup.
Too much HFM'd = smooth shift and TC lockup, but possibly full power slippage and wear(very noticeable on tired trannies and those requiring lesser HFM'd fluids).
Too little HFM'd = abrubt shorter clunkier shifts along with TC shudder. And, if the tranny times the shift, excessively grabby fluid could cause a line pressure drop, more slippage, less holding capacity, and increased wear.
You should also reset the TCM when you switch or change your ATFs. This will eliminate any confusion caused by the learned/adaptive transmission parameters. This is usually done by leaving the battery disconnected overnight or with a obd scanner. Reference your FSM.