I do not agree with that at all.
4 strokes do not run as well inverted without an onboard glow. It does matter orientation regardless of how well tuned a motor is. The fuel is being dumped into the carb and gravity will pull it into the cylinder head(and accumulate) which can cause vapor lock or cooling of the plug too much to allow proper ignition.
For any 4 stroke engine mounted inverted, an onboard glow system is a good idea. One of the main benefits is keeping the motor RUNNING when throttling down to idle when trying to land...and then IF necessary...being able to throttle up quickly without motor hesitation(loading up) or even stalling out and quitting.
Aside from keeping a motor running at low to mid throttle range(depending on where you set the onboard glow to stop providing heat)...it also makes it 100% easier to get the motor started to begin with sicne you dont have to fuss with a glow stick and getting under the cowl/engine simply to hook it up..and then remove it once the motor isw running.

An onboard glow provides smoother idle and also lets you lower the idle rpm without the motor stalling out compared to the same motor not using an onboard glow.

Ive learned my lesson so to speak regarding the use or lack thereof relative to onboard glow. Sure....I'll fly a 40 size warbird like a kyosho me-109 with a saito 72 in it inverted without onboard glow. Why? Cuz the plane is light and if the motor quits, the plane wont become a unpowered brick.
However, in the case of higher wingloaded planes such as this CMP ME-109, if the motor dies, especially at a bad time, your in for a hard time and probable crash/damage.
Hell..ive had light Hangar 9 warbirds with saito 100's, 125's properly tuned simply quit on final approach prior to making the runway simply because a glow plug starts to fail and no onboard glow means heat dissipation on the cylinder head resulting in a motor that dead sticks. The result? No thrust when your already throttled down = a wing stall and spiral into the ground = smush.

An onboard glow means piece of mind for me and usually saves an airplane from occurances similar to described above.
Theres no way in the world Id fly my 80" P-51 with a saito 220 in it without onboard glow. Why risk losing a $1500 airplane for a part that costs $60. Same for my 95" B-25 with twin 170 radials.
Motors do load up in the air and can go lean even under the best circumstance. Also...fuel is another cause for deadsticks. As fuel gets older or even if somehow it gets water in it, that will cause issues. What sounds great on the ground can turn nasty in the air. yes...it can and does happen. An onboard glow can keep a plug firing even with somewhat questionable fuel.
Ive got a TF 60 size P-51 with a saito 125 in it. On the ground, the motor sang and ran beautifully.....giving 9000+ rpms. However, once in the air....the plane definitely didnt act like it was running well at all. The motor was properly tuned, rpm checked, richness/leaness and all that nice stuff check prior to takeoff. It had even flown before so i knew what it should have flown like. But...had a batch of bad fuel and it ran like a dog once airborne. Had there not been an onboard glow on it set to run up to 3/4 throttle....the motor would have deadsticked. I know this cuz I couldnt throttle above 3/4 without the motor starting to sputter.

id recommend you get the mcadaniels onboard glow from horizonhobby. You can set it to any throttle setting you want and has an indicator light on a wire extension for you to mount wherever you like for easy viewing so you know its on or off relative to throttle position.