On paper this team should be going after one of the closers to strengthen the bullpen, Helsley, Saurez, Diaz all available as FA's
So volatile though, and it seems as though you rarely get the bang for your buck when you pay big money for these guys, at least in terms of fWAR. But is fWAR a good gauge for evaluating a relievers value? Astros paid $19 million AAV for Hader last year and he only put up 1.1 fWAR. The guy is nails though.
And as for volatility, look no further than Helsley himself who was an excellent reliever for 3.5 seasons and then after being traded to the Mets last year, just straight up shat the bed.
I'll ever forget Brad Hand being a good reliever for a long time, coming to the Jays mid season and blowing chunks down the stretch while the Jays missed the playoffs by a single game with 91 wins. Then he went to free agency, signed elsewhere and immediately went back to being a good reliever again.
If Yimi comes back strong and can stay healthy, he'll be a big boost. But if they were to pay for Helsley and he was as good as he's been in St. Louis, I think it'd be worth it. Tough gamble though and could be just wasting payroll. If payroll isn't really a worry though because they are going all in I'd be inclined to pay up for a closer like that and take the gamble.