Are they a bit risky, ie might come loose? I need a new stem and would like to try different heights but can’t really buy several different stems!

Any recommendations? Thanks.

As a temporary measure, and assuming you’re not going to do anything too mental on it, it’ll probably be okay.

Do you not have any steerer tube above the headset to play with by swapping spacers around?

Ask at your LBS. They may have one that they can lend you in order to determine the correct size. Of course, you’ll then be obliged to buy your new stem from them…..
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Hi GW – * waves *