Quick A: No
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Is it guaranteed that all compliant compilers have the same experimental features?No, experimental features are optional.Are experimental features prone to big changes that make them unreliable?Yes, the C++ committee might even decide to abandon a feature or in the process of standardization a defect might come up that would force a feature to change.
Generally, it's not a good idea to depend on experimental features. Experimental features are exactly what the word says (i.e., to experiment with).