[Meizu MX] $or$:
I want to answer your question by comparing both phones in each category.

Design:

I started with design part because, for me it's very important part. I like meizu pro 5 design much more than 6p not saying 6p is not good but, 2.5D glass with looking similar to Iphone in front is not a bad thing in meizu and better than 6p here. I prefer Fingerprint as a home button on meizu at the front much more than in 6p at the back. ( Not to mention how innovative home button of meizu will change the way of using this phone when you getting used to it and you cannot compare it with any other android phone). Also design of meizu at the back is also more beautiful in my opinion as it's a little similar to htc one series. Also 10g less weight in meizu should be a little more suitable in hand.

Camera:

About camera in meizu it does pretty decent job in good light maybe even better than 6p specially better in detail comparison but, in low light you should either use manual mode or accept quality of auto mod which is not bad but, differently 6p is better but, not much better.

Selfie with front camera is definitely better (more detail) in 6p but, for internet both do good job here.

Processor:

The main problem in 6p is qualcomm 810 processor which is a big no for me specially compare to Exynos 7420 which is arguably the best in the market for now (even compare to karin 950) and you will never feel a hot phone in your hand or lag due to hot temperature of cpu and much more energy efficient than Q 810. (Not fan of Antutu benchmarks but, recently Meizu take the crown from Huawei karin 950 chipset in Huawei Mate 8!)

Softwere:

On the other hand meizu apparently is new to world market and cannot support their phone like google but, in future with custom roms it will be okay I think (do not expect near future!) Meizu does not come with unlock bootloader and apparently there is no way to unlock it and it may take so long to either someone manage to unlock it (very difficult + lack off good developers due to less popularity of meizu and the phone itself) or company give us a way to do it so, do not except support of developers or company like 6p. Meizu will definitely upgrade meizu pro 5 to marshmallow but, time is unknown.

Also if you really like pure android experience which I don't! heavily skin of Flyme OS on top of android in meizu may become a big problem for you. Lack of app drawer or design of home screen or even default apps are not a big deal as you can get a good launchers now a day specially with htc sense launcher and apps but, other part like setting menu and notification drawer and etc will be always the flyme one!

Screen

Comparing the screen, there should not be much differences as both phones using very similar amoled technology and panel. Yes 2k vs full hd but, 2k display of 6p is not as good as samsung new flagships like gs6 or note 5. Brightness of both phones are almost similar. I don't think you will notice the differences here in display part in daily usage because, differences of 2k displays are not very recognizable in human eyes in phones bellow 7" screens. But, if it does for you it's just a little more sharper but, not better in contrast, color and etc.

In 6p you will get gorilla glass 4 which is better when you drop the phone and can manage much more pressure here but, not as good as gorilla glass 3 (meizu pro 5) in scratch resistance part. If you use screen protector no problem here for both phones.

Audio:

Yes 6p has dual speaker in front which is more suitable when watching something or listening to musics with speakers but, meizu on the other hand support Hi-Fi audio so, provide much better quality sound specially when you plug a headphone which 6p was unfortunately poor here.

Hardware/Connectivity/Network/Battery:

Lack of memory support is again a big downside of 6p compare to meizu plus 2 sim in meizu vs 1 in 6p (in meizu 2 sim if you don't use sd card) .

For connectivity both doing great and not very different here. You have more 4g bands support in 6p but, if you don't live in USA you will not loose here. Meizu definitely is much better in battery part as you know so, no more words here. Also meizu charge the battery a little faster than 6p specially if you charge 6p with retail charger in it's package which the plug is weaker than meizu fast charger plug. (No need to buy faster plug in meizu).

Okay I don't know if I left anything else and hope it helps you to choose the best option but, personally I will choose meizu here as you mention the price of 6p I don't think it wrote 200 euro more just for a little better camera, speaker and screen VS it's downs. But, if you cannot live without latest version of android and faster support of google or with Flyme OS of meizu better to go for 6p. ( The only real downside of meizu compare to 6p currently before unlocking the bootloader of pro 5)