I think I have tried most things that adds sound to my conventional fleet over the last 5 years.
I have a 2005 era Alaska Railsounds diesel sounds boxcar, sounds good.
I have a 2000 era Seaboard boxcar with Railsounds, sounds good.
A 26871 style tender from 2000 era and one from 2004 era, both are good.
2 of the 2426RS 19833 tenders with Railsounds II. One Railsounds II tender with the 18040 set. All are good and work well. I use BRLT battery replacements in these. One was "almost" new and had a 9v battery in it that leaked when boxed for 8-10 years. Luckily the battery was in the "coal" area far from the electronics and was able to fix the damage.
I have had 4 of the 1993 (used) era 2671 style tenders with sounds. 2 bad, 2 volume control would not work. On the two that would work I found that when I redid the "wire nut" connections it worked much better. Volume control still never worked though. I think they were at "full". I now stay away from the early ones.
And then there is the first gen "Mighty Sound of Steam" A white noise sound for chuffing and an OK, but not great whistle. The grand kids love the whistle though. I got it working on my 783 engine and tender, but never try these systems until you take it apart and inspect it. The double back tape that held the board was rotted away on mine and If I had powered it, the board would have been fried.
To fix the 1993 era systems I used some newer "Railsounds" kits. I like the ERR soundsystems also. I have a couple of those installed.
That's my experience.