Vista hearing aids are not likely to be a hearing aid model that can be fit using
Unitron TrueFit (whether version 5.5.1 or the newer available
Unitron TrueFit 5.8.0 version). Here's a clip from the DIY School Hearing aids (v2.2) PDF File named (Unlocking ReBranded Hearing Aids) which is alphabetized by manufacturer, so you will have to scroll down to find Unitron;
Install Tip: Ignore the offer to create a professional account.
AuraFit/Aura:fit 5.5.1 is a version of Unitron TrueFit for ReBranded Vista
Models (Vista V, Vista B, Vista DX, Vista D, Vista Basic +, Vista T, Vista N, Vista)
AuraFit Relate/Aura:fit 5.6 is a version of Unitron TrueFit for ReBranded Relate
Models (Relate 4.0, Relate 3.1, Relate 3.0, Relate 2.0, Relate)
Hansaton Scout 5.7 is a version of Unitron TrueFit for ReBranded Hansaton
Models (flow+, AQ sound SHD, sound SHD, AQ jam SHD, jam SHD, beat, flow, soundHD, jamHD, sound, jam)
audifon audifit4 is likely ReBranded Unitron; for very old Legacy models (eox, elia, prado, switch, vico, arriva, avero, sueno, axia, avacio, loon, aueus, allegro, assista, DiWise, HC, S 437, S 424, ACO II, H 150, H151, H152).
audifon audifit v5.6 is likely ReBranded Unitron; for very old Legacy models (rega, kami, sino, faro, saga, libra, miro, vico, sueno, via pro).
Audifon Audifit v5.8 (not yet found) is likely ReBranded Unitron; Models (lewi R, lewi S, risa R, Risa S)
Aura:fit AudioNova v5.7 (or 5.6/5.1) (not yet found) is likely ReBranded Unitron; Models (AudioNova B, AudioNova DX, AudioNova D, AudioNova T) and (NovaSense Elite, AudioNova Basic+, NovaSense Basic).
Unitron Au ReBranded models: (fitting software not yet found). Models (Au B RT RIC, Au B R RIC, Au B PR BTE, Au B 312 RIC, Au B 312 Dir ITE, Au B 10 NWO, Au 3 10A Omni ITE, Au 3 W 312 Dir ITE, Au 3 P Li BTE, Au 3 R 312 RIC, Au 3 R Li RIC, Au 3 R Li T RIC, Au Basic+ M 312 BTE, Au Basic+ UP 675 BTE, Au Basic+ P13 BTE, Au Basic+ RIC)