I have no videos to show (and even if I did, I wouldn't advise you put much stock in anything on YouTube; YouTube compresses the audio so much you really can't gauge anything from there anyway) but I've swapped necks on many guitars, in every combination of Warmoth's 'pro' construction to Vintage Modern/other brands' standard construction, and 25.5" to 24.75" (and 25" and 24") conversion, and done so without changing anything else about the guitar. (Including the wood choices of the necks.) So I feel I have a good handle on what changes to expect.
Tonally, I've only ever noticed the difference between native 25.5" and conversion 24.75" when played clean and with 'American' style amps, like Fenders and Mesas. There's a little more 'snap' to the 25.5", or conversely you could say that the 24.75" is a little softer. It's consistently been a very similar change in sound as changing a guitar from a maple fretboard to a rosewood one, or vice-versa, or changing between common frets and stainless steel or gold frets, except unlike those the scale length is an effect which I only ever hear with those clean, brighter amps. Unlike fretboard or fret material changes, the scale length change disappears once there's a modicum, or with any 'British' (e.g. most Marshalls, Orange) or balanced (e.g. Blackstar, Marshall JVMs) amp.
The feel is the main difference, by far. Less string tension means easier bending and vibrato is both easier to do and has a broader effect. I've not noticed any change in tuning stability or set up stability, though I can't say I ever tolerate unstable guitars anyway.
If you like 24.75" scale, go for it. The difference in sound is there, but it's minimal—inaudible in many scenarios—and can be easily compensated for with electronics. Getting the feel you want is far more important and can't be compensated for in any other way.
For the Pro construction, they definitely have a much brighter sound. Keeping woods, frets, and scale lengths the same, I've swapped from Pro necks to standard necks (which Warmoth calls Vintage Modern; every other brand uses it as standard) and the sound has always become smoother. The low end doesn't change but you get a lot less treble when moving from a Pro neck to a VM/regular neck, and vice-versa; changing a regular neck for a Pro one sees a big increase in treble. Unlike scale length, this is a change which is audible regardless of amp, tone style, or play style.
The more important difference to me, personally, is the feel. Pro necks are far stiffer, both in terms of their stability and also in the way the vibrations through the neck feel in your hand. Pro necks are real bone-rattlers; don't use one if you have RSI or arthritis in your fretting hand! If you think about the difference in feel between a mahogany neck and a maple neck, moving to Pro construction is that same difference again on top.
They're more stable, for sure. The side adjust is a pain in the arse, not very effective, limits what bodies you can use the neck on, and is really ugly and feels bad under the hand. However, once set up the first time I've never had to make a single adjustment to any Pro neck. You do it once and can forget about it. That's about all there is to say about that.
They're also a lot heavier. It depends on the neck profile, woods, and tuners used of course, but when changing like-for-like, Pro necks are consistently a third heavier than their regular counterparts.
As for why Warmoth won't do conversion necks without the 'Pro' truss rod, who knows. Maybe they bought a huge job lot of those and they're still working to get rid of them. Maybe their marketing spiel works for most people and they sell just fine as they are. All I know is that I, personally, would buy more necks from Warmoth if they offered more options with the Vintage Modern construction instead of reserving all the good stuff for Pro construction, as would more of the people I service, repair, and piece together guitars for.
Whether a change in tone or feel is good or bad (or irrelevant) is entirely down to personal preference, but for what it's worth, I've ditched all of the Pro necks I've ever ordered, and replaced them with regular-style equivalents. I kept thinking I'd come around on them, but I never did, so I just stopped trying to live with them and got rid of the whole lot. Additionally, in the last couple of years I can recall only one instance of being asked to fit a Pro neck to a guitar and not then being asked to replace it with a normal one. Everybody else around here (actual here; not 'here' this forum) tries 'em once and wants to switch back, too. For myself it's the weight and the side-adjust which I can't live with; for everyone else I've dealt with it has mostly seemed to be due to the tone. In any case, I still order bodies from Warmoth but get all my own necks from other parts companies, now, and I think I'd only order a neck from Warmoth again if it was a 25.5" Vintage Modern construction; I prefer 24.75" and 24" so I myself am basically guaranteed to never be buying a Warmoth neck again, personally.
Your mileage may vary. As this forum shows, clearly there are loads of people who like the Pro necks.
