How useful double and triple position players are?

I use a lot of different formations, setups, which then require players for all positions. That is why I like double and triple position players which enable us to change formation or player's position during match without using substitutes. Recently I became more cautious about players form and noticed that most of these players can play only one position effectively. That means their average form is around 7 on one position and 5 of other (trained) positions.
So I had:
AMC-ST-MC who played good on ST (8-9), but horrible as MC (5-6), average as AMC (7)
DC-DR who was good for DC only, but had constantly 5 as DR although right footed
DC-DMC for DC (7) only, 5-6 as DMC
ML-AML for AML (8-9), 6-7 as ML etc.
It is frustrating for me to have player for 2 position, but useful on only one, just like single position players. It is even more unfair for players who train that 2nd or 3rd position. Why should someone spend 50 skill points on new position and then realise that player is useless on that position?
Similar problem is with players who are in great form, then they learn special ability and then form suddenly falls down - became useless.

Have you noticed same problem with double and triple position players?

I always try to get defenders who can play DL/DR as well as DC, but other than that I'm not that fussed about double positions.

I normally swap between a 4-4-2 formation to a 4-4-1-1 or a 4-4-2 diamond so bar one player that needs to be a AMC (I try to get a ST/AMC if possible) and one that had a DMC (normally find a couple that have DC too) I am more than happy with having players with the more "traditional" roles.

I don't think I've ever used the DML or DMR spots, simply as I feel I'd have to play both flanks and don't like that idea - and for the same reason I very rarely bother with AML and AMR unless they come with my ML/MRs as a rule.

I aim each season to have -

2GK
3 DL/DC
3 DR/DC
2 DC/DM
2 ML
4 MC
2 MR
1 AMC/ST
2 ST

Then I have a spare spot to keep my youth player before selling him. Occasionally I carry an extra MC for cover too. Not all my defenders have duel, but most do so I can get away with one or two just having one role, as long as that role is DL, DR or DC.

Very recently I hav noticed dis. Its another bug i suppose

so far
DC + DL/DR good
DMC + MC +AMC fail
ST +AML so so
MC +ML no
MC + MR no
AMC/AML + AMR yes
DC + DMC I 'm not sure because DMC position is bugged.
Now I 'm trying to play an AMC/AML as MC (oop) to see if it's working because MC position is also bugged.
So far in 3 games L/CH/C and one f, he got 7.

@nikolgiorgos From my xp AMC works better if he is offensive minded than pulled back on mc. I have had few am-mc's and am-st's and they react better in offensive part of game, although sometimes it's individual.
Today I had league match where my amc got 6 in 4411 formation. He had blue arrow. Then I tested him without arrow in friendly and he got 7. Maybe it is usuall oscillation, but I believe that removed arrow had impact.

Positions are only part of it, there's also orders, formation and opponent but putting them aside.

I've had AMx/Mx that can perform in both roles, in either 1 or neither, same with AMx/AMC, same with DL/DC that can do both, etc. I currently have 1 DC/DMC that excels in both and another that is better as DMC and average as DC (but can also do a job as MC).

Additionally, without the roles, I've had good MCs that make good DMCs and others that make good AMCs and on my OMA team I had a good striker that made a good AML and AMR. (I tried another ST as AML today and he was utter crap.)

I've even had a left footed AMR/AMC in the past that was good as AMR but crap as AMC....so I trained him as AML as an experiment and he was crap there too.

There are no hard and fast rules. Additional roles don't mean a player can play that role, it just means he can try without penalty. After all, some single role players can't play there sole role either.

If you want to add an additional role then try the player there first - even with a red penalty there should be something encouraging there, if not don't do it.

Actually I was hopping to have some more influence in the process, let's say to have a MC more def. (with blue arrow) and the other more off. (with red arrow).
Same in DC, one with blue arrow, to stay behind and one more free, to move forward in corners etc

I prefer double and triple position players but the problem is they are sometimes only good at playing one of the positions, not all. So you have a challenge of trying to figure out which is his best position so the second or third position is redundant...

I have also notice that even if they can play many positions they do have a favorite position.
But having a wing AML/AMC/AMR on the bench for autosub when you can't watch the game is really nice same with DR/DC/DL. If you don't have that you risk having a sub out of position.
But on defense i normally stick with a DC/DMC autosubber.

I wish we could set up a auto sub for every player on the field. Who in their right mind would throw in a right winger when a left winger get injured and you have a left winger on the bench? :)