Discretion matters at this level, so ask how a practice handles approvals, legal review, and a company's communications team. A good fit works inside a company's policies while building a reputation that stays yours when you move on.
The directory has three vetted practices that list executives among the clients they serve: Mashman Consulting Group, JaKe X, and Orchard Strategy. They are based in Barcelona, Cataluña, Little Rock, AR, and Taipei City, Taiwan, and they are two independent consultants and one consultancy.
As for how they work, two offer done-for-you work, where the practice does the work; two offer done-with-you work, where the client works alongside the practice. Of these, two work with clients remotely anywhere and one works both remotely and in person. Their working hours follow Central Europe, US Central, and US Eastern time. Between them they work in English and Mandarin. Their price tiers, $$ to $$$$, are shown on the listings on the same scale as every practice (what the tiers mean).