Thank you for the compliment, same to YOU !

Savings depend entirely on how much one spends on UA tickets at UA websites/apps. I’ve only booked with a companion 2 or 3 times but IIRC - yes, once the “Promotions and certificates (optional) - Offer Code” is entered it will apply to all applicable tickets purchased. It’s not applicable to all flights, IME ~75-80% of flights are discounted, without apparent pattern. On a search results list of 40 flights, all might be discounted or only a few or none.

I’m not a shill and have no vested interest in VA other than having had good experiences and disliking seeing a company that I appreciate get bashed. Granted you won’t save thousands of dollars and whatever savings you do receive are cumbersome to obtain. Part of my motivation is the small satisfaction of giving UA, a company that I hold in much lower regard than VA, a little less money. I’d gladly pay VA $50 a year if the only savings were $50 less to UA.

(I also sometimes will continue to do business with a company based on past benefits, not necessarily possible future benefits. I’ve been a member of AAA for 40 years, membership fees initially paid for themselves in paper maps, Tripticks and 2 or 3 tows. I haven’t looked at a paper map for 10 years and recent new cars/auto insurance include towing but I still pay AAA dues. I joined AARP years ago mainly to save on hotels and rental cars. I haven’t rented a car in 5 years and have since found better ways to save on hotels but I still maintain my AARP membership.)

I joined VA 9 years ago on a 1 month trial for $5.00. A month later 1 year at ~$51, then 3 years at ~$32/year twice. Upon my request during COVID in 2020 they extended for 6 months. A year ago I renewed for 4 years at $35/year plus $20/year for their travel protection package. They do send frequent renewal offers with different renewal rates.

My $$$ spent on UA and VA savings are (approximately): 2014: $6,000/$190, 2015: $6,200/$210, 2016: $6,000/$150, 2017: $5,200/$165, 2018: $3,200/$90. Stopped keeping track in mid-2018 upon achieving lifetime status and transitioning to mostly award tickets. Savings average ~3% overall as only base fare is discounted and not all tickets are eligible.

Probably didn’t save very much in 2019 and 2020. In 2021 I started being solicited by AmEx for targeted NLL card offers (including multiple biz plats) and decided to use UA TB for the annual $200 Airline Fee Credit. That’s why I was so pleased a few days ago when I was able to buy a ticket on UA website using both VA discount and TB funds, saved $20 on a (total) $393 ticket, as described here.

YMMV.
A common expression in (my) medical school. We always heard it as "When you hear the sound of thundering hoofbeats, think of horses, not zebras!" My corollary, in good part based on my specialty (Emergency Medicine) is: “but we get paid to be 100% certain it’s not a zebra”.