For large and active dogs, the weight of current evidence and specialist practice has drifted toward TPLO, and it is now the default recommendation at most referral centres. But TTA in the hands of a surgeon who does it constantly beats TPLO in the hands of one who does not: technique familiarity moves outcomes more than the acronym does.
Both operations solve the same problem by different geometry: TPLO levels the tibial plateau so the femur stops sliding; TTA advances the attachment point of the patellar tendon to neutralise the same force. Both are established, both work, and complication profiles differ more by case selection and surgeon than by procedure.
The useful questions for your quote: which technique does this surgeon do most, why do they recommend it for this dog specifically, and what are their own revision numbers. If two clinics recommend different techniques for the same knee, that is a classic and cheap case for an independent opinion.
Send what your vet said and quoted. A veterinary surgeon reads it and comes back to you with what they can do and what it would cost, before you pay anything. A written second opinion is from $250.
Send the case, hear back from a surgeon with what they can do and what it costs, and only pay if you go ahead.