Pickle_Rick, not sure if you're still looking for clubs. I'm late to this post, I know, but I'll give you my input on a set of used RSi 1's. I found a set for about 1/3 of their current resale value due to some damage to 4-6 irons. As noted the Taylormade's which used face slot technology have issues with faces caving near the slots and sometimes the slot material falling out. This the case with the 4-6 in my set - there is some caving to the faces but slots are still in tact at this point, 4 is worst and 6 is very minimal. From my research this happened to almost all the generations they put out but there may also be some effect attributed to the player as some reviewers say they never had any issues. However, it seems it happened more often than not.
I've had my set at the range multiple times and have played two rounds with them. I have not noticed any further damage to them to this point. Clubs are forgiving, balls feels good of the club, and I did gain about 10 yards per club compared to a 2006 set of Tommy Armours I had previously. I have not noticed any "mishitting" due to the damage. That is not to say they won't continue to get worse as they are played more. Because they were so discounted I grabbed them with the thinking that I'm getting new technology (they came out in 2015), I don't use a 4 iron that often, and at my skill level I don't know that I would significantly notice an effect due to the damage. I shoot in the 90's to mid-90's. Also, if I continue to get better where they are affecting my play I can upgrade to another set and feel that I have gotten more than my money's worth with the RSi's. That's my logic anyway. Could be flawed.
So, if you did find a set of RSi's just keep in mind the faces will most likely start to cave on the irons that have face slot (down to 8 iron). If you find a set that is already damaged and are super discounted to a price you are comfortable with I would consider buying them with the understanding of what you are getting. Sorry again I'm late to the post and this may be no help.