bmwtechguy says it well. When an oil meets API certification, it only proves that it meets MINIMUM standards. Certification costs hundred of thousands of dollars, restricts the additive package, discourages updates to formulas, suits the large sales numbers of major oil companies (not small companies), etc.
As with any small business, boutique oils have the freedom to be better or worse, use cutting edge research or outdated technology, and offer performance that is overpriced or underpriced. Never rely on customer testimonials alone. Look for a solid reputation among oil nuts (that's us), independent testing, used oil analysis, expert consultation such as Terry Dyson, etc. Boutique oils aren't for everyone on BITOG, but neither is Pennzoil conventional.