Patients generally prefer less invasive sample collection methods, which are also easier to use at home. That said, we are considering launching a blood-based collection method, too.
Both saliva collection and cheek swab are reliable methods for whole exome sequencing. The combination of sample collection, sequencing and variant calling have to comply with CLIA and CAP, it's a binary cut-off. We wouldn't be able to (and wouldn't want to) report back results for which we can't assure quality.