MeSince only charges the validation fee. That means which type validation you choose, the relevant signing certificates are free, and the number of them is unlimited. Specifically, if you are using an email address on N devices, then MeSince will issue N signing certificates to configure on those N devices without charge, this is same for free validation and charged validation.
So, for the question, yes, MeSince will not charge fee on certificates and no limit for the number of certificates. For organization validation, the validation service fee is US$89.99 for one year, which is the fee for validation. All your company employees will have V3 identity certificate for free even your company have more 10K employees, and also no limit for all devices used in your company. No number limits on employees or devices, all certificates are free, just charge the identity validation fee.