As per my experience we have been using Zendesk and didn't face any issues either with technicalities or support.

Let's first of all position who are the audiences for an Immigration Firm. If we classified immigration into:

1- Skilled immigration (Employees), and
2- Business Immigration (Investors)

Skilled Immigration fees are affordable and due to the high competition the Professional Fees are competitive and payment plans are there to attract more clients.
HINT: Despite that, Applicants have to conduct an overall check up about the credibility of their meant immigration consultants.

On the other hand, Business Immigration which involves a bigger amounts of fees and investment are treated somehow different.
As per the country of destination and the route of immigration which is almost limited between Property Investment, Financial Instruments Investment and Donation varieties of payments plans are offered to attract Investors.
In other words, Legal Fees and Processing Fees are considered as a small portion of the Deal which doesn't shape a concern to Migrant Investors rather than the tool used for immigration and the success rate of that firm.
HINT: When choosing an immigration program it is preferable not to pick Immigration firms relying only on RCBI programs (Residency & Citizenship by Investment) as the risk lies in the project continuity as per the demand which to some extent can delay the whole immigration files under that project.