I was planning on running both at the same time; what are the downsides?
There is nothing wrong with doing both at the same time, I am old fashioned and also older, so I look at my kidney-toxicity and blood in the urine, Fina and winny are in my opinion harder on your kidneys than deca and test, so I just split them up.
Technically, Tren/Fina does not hurt your kidneys and is actually mild, probably, wrong word, but
It is a kick ass anabolic, and you will see great gains.
If there were some great reason to mix them, then I would say mix them,
But either way don’t run them forever, 6 weeks, max, Tren/Fina makes me more aggressive,
My favorite cycle based upon past experience and muscle gained fat lost, is
Fina
Winny
D-bol
Test
Primo
Did the Fina, winny and d-bol all at separate times.
Had sides, but felt awsome, looking forward to this cycle again.