For plastic/ fibreglass fender wearing Tontis , a fork brace can certainly help. The ones with stainless fenders ( 750S3, T/T3/T4 G5.Convert) already have the fender brackets that suffice as fork braces, so for the sake of Guzzi frugality, why would someone toss what already works and spend money to correct fork flex?
Both the Tarozzi and Telefix are nice pieces, but they stiiffen up fork motion both to and fro as well as normal , small vertical movement variation, between left/ right legs that, to me are necessary for supple fork action. The later factory fork brace equipped Guzzis allow some vertical movement variation so apparently Guzzi engineers also took that in consideration. SP with Cali3/SP3 fork conversion ref. pic below
YMMV