GY 521 + GY 271

Hi all,

I got a question. I ordered these 2 breakout boards to have some fun.
I noticed that the GY521 in the schematic on the SDA and SCL had pull up's to 3V3. I have seen quite a few tutorials about this breakout board, but I've hardly seen anybody using logic level shifters?

In the GY 271 I do see that they use MOSFETs to do some kind of logic level shifting.
Anyone has experience using these breakout boards?

Then I am planning to put some more sensors on the I2C bus. Is it needed to remove the pull ups from the breakout board? If the first breakout already has 4k7 pull up resistors?

Thanks for clarifying!

keep total pullup in range 2k..10k to be safe. =>> 2x 4k7 in || is OK

Ok thank you! as soon as they become more I will have to remove the Pull ups.
How about the logic level?

They can be supplied by 5V. If I measure the open SDA/SCL lines and they are 5V can I safely connect them? If they are 3V3 I need the level converter. Am I right?

So I got the GY271 working. And no surprises it came with the QMC5883L. Now the thing that matters for me is the magnetic heading. I understand that the QMC5883L is not much more than a flux sensor and it needs to be compensated for any horizontal and vertical offsets. Does anyone have a good recommendation for a proper replacement?(including accelerometers?)
The GY521 is an accelerometer but not on the same board. If I would use that probably my calculations would still be way off...