Should long form be used for investments in a mortgage loan company.

Instructions for 5500-SF say 'Have 100% of its assets invested in certain secure investments with a readily determinable fair value...'.  I have a client who has an investment in https://truelinecapital.com/.  We get statements showing the value is unchanged and all interest payments are deposited to another plan account.  I'm wondering if I should be using the long form given the nature of this investment.  Any thoughts?