I did the same thing when I replaced my 25 foot LMR400 UHF-UHF feedline with FSJ4-50B N-Male N-Male, same length. The heliax I got was factory made. I got mine from eBay as a NIB New Old Stock, I paid 35 bucks for 25 foot with 2 preinstalled trimetal N-male connectors, which are like 29 bucks a pop.
To give you quantitative figures: The antenna feedline connector at the base now reads a near perfect 50.03 Ohms impedance, and the return loss is -38dBm... as expected range now is measured in tens of miles, too, as opposed to the LMR400 which had an impedance of 43 Ohm and a -28 dBm return loss, while not bad, range was at best 10 miles.
There are people here who can also make these cables. I just wanted a factory cable with the datasheet and sweep chart to ensure I wasn't getting a dud.
The keyword on eBay to find a N to N heliax is "PNMNM" if you type that you'll get every cable on eBay that has N-male (NM) to N-male (NM) There are a ton of listings, just look for FSJ4-50B.
Do you suggest the FSJ4-50B over the LMR400?
Where can I go to look at pricing and to purchase? Thanks!