I bought a Hero 616 pen several years ago and was unimpressed. The construction looked shoddy and the aerometric filling system would only hold a very small amount of ink.
Years passed and I decided to try the larger 616 "Doctor" version (also called the "Jumbo"pr "Regular"). When I compared it to my old 616, I immediately noticed a difference between the two pens.
The 616 "Doctor" did not have the cosmetic flaws of my original pen and seem to be built better. The aerometric filler worked flawlessly and held a generous amount of ink. It is a different pen.
After doing some research, I discovered my original 616 must be a counterfeit. (See link below.) Buyer beware.
The pen is around 5.5" long and it weighs 18 grams when filled. A very light pen and comfortable to hold. How does the "Doctor" write? It has a very smooth fine nib that is one of the best I have ever used. Just what the doctor ordered!
I have never used a vintage Parker 51 (the pen that the 616 design is based upon) but this is one great budget fountain pen. You can find it for less than $5 on eBay (even less if you buy in quantity) and it is well worth the price.
More info on counterfeit 616s here.