If you ever want a cheap, new alternative to Parker 51 style pens, the Wing Sung 601 is actually really good. Most of the chinese imitations are rubbish, but the Wing Sung 601 is fantastic. Obviously a real vintage Parker is going to be higher quality, but if you like your Parker but also want a backup you won't be terrified of losing or breaking these pens are great. The 601 is heavily inspired by the Parker, it is clearly an attempt to make a modern version but it also isn't trying to pass itself off as a real Parker 51 with fake branding or anything so it doesn't feel tacky.

Also the Wing Sung 698 is a $20 piston filler pen that is very high quality (easily beats TWSBI Eco in my opinion in build quality) and the nib can be switched out with a pilot nib from a metropolitan, plumix, or any of pilot's other stunning nibs (that they stick on ugly pens to try not to completely undermine the market for their expensive pens lol). The fit is perfect, just like an official pilot pen honestly. I use a Wing Sung 698 with a pilot italic nib (from a plumix or a metro I can't remember) and over the years it has become my favorite daily driver pen that I can stick in my pocket and not care if it gets scratched up.

Here are random ebay links to the specific pens because it can be overwhelming even finding them to buy online. I recommend buying from the ebay seller jewelrymathematics as they are very trustable and focus on carrying chinese fountain pens. I ABSOLUTELY advocate for buying nice fountain pens but also only having expensive pens that are hard to replace is stressful, having some cheap but high quality fountain pens means you can enjoy the hobby in a lot more contexts.

Wing Sung 601 https://www.ebay.com/itm/234861926628?hash=item36aedc98e4:g:-ssAAOSwH8ta6B2H

Wing Sung 698 https://www.ebay.com/itm/234007412192?hash=item367bedbde0:g:KB0AAOSwBwBZkszL

I personally prefer the clear version with silver accents and a white cap but jewelrymathematics doesn't have it, this is an example of my fav 698 https://www.ebay.com/itm/275375673933?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=frlHIXeQQGu&sssrc=2047675&ssuid=KbfDVa6JQrq&widget_ver=artemis&media=COPY