Well, if you evac it into a machine with 134A, yes. You will destroy their recovered refrigerant...but seeing as how 152A comes in air duster cans, you can just release it into the atmosphere and it is no big deal.
Initially I had 134A in that 300E as it was all I had on the shelf. It leaked out, so that is when I tried the 152A. Cheaper and worked better. R12 would be better, but for $15-30 for a 12oz can versus $2-5 in...it was a no brainer for me. The car cooled very nice for me.
Make sure the condenser and radiator are clean. Need to pluck the rad to pull the condenser far enough back to pull the dual aux fans. It is worth the hassle. Also, the only fan clutch that worked for me on the M103 was the Sachs. With no air flow over the condenser, you will have weak AC always.