I find it's less hassle to program a funcard than manually upgrade keys (lazy sod!) for most other channels. And for a few channals on 5E (Sirius) - if you receive it - you need a fun (eg Tickets).
Otherwise it's down to the strange interactions of your receiver, the MR and the funcard (or the file you use for it). For example, until MR rev 1.055, I had been unable to open any of the Dutch channels (eg Ned1, Ned2, Ned3) on 19E (Astra) with or without a funcard. MR1.055 will now open these channels but only without the funcard inserted!
I haven't been around this hobby that long but the one thing I believe I've learned is that there are no definitive answers unless you can compare notes with somebody with exactly the same equipment as your own. And I probably haven't answered your question either!