It’s not that great a deal. It’s basically 4 days for the price of 3 but the difference between 3 and 4 day tickets is only about US$25 anyway. You can do better by purchasing from reliable resellers like aRes Travel, Undercover Tourist or if they have stock, Last Minute Travel Club. For LMTC you have to call but their 5 day tickets are only about $3 more than the 4 day so even better value. For comparison, my 5 day parkhopper tickets were US$332 or A$485 each for adult tickets. That’s way cheaper than a 3 day ticket on the Disneyland website where they are US$355. 5 day tickets on the DL website are US$395.
Another option I have heard of but not tried is to ask your travel agent to check prices with a wholesaler called Beds Online rather than whatever wholesaler they are using. That’s where my vouchers ended up coming from through LMTC and I’ve heard they are generally a lot cheaper than other industry wholesalers.
All the best.