I repair a lot of cello cracks amongst other cello repairs , esp on student instruments. My approx to student instruments varies, as they need to be cost effective because of the instruments value. For this reason I get a lot of repairs from schools and parents alike, for which a classical repair might not be possible.
If the crack is clean, that is, not too much fracturing of the wood it is possible to do a near invisible repair, though often this is not the case, due to the nature of the finish applied to student instuments (a sprsay nitro or acrylic that often flakes).
Below is one repair that turned out quite well. Here you can see a sound post crack under the bridge, The origin if this is that is was an imported instrument never setup in, or for, Australia and the sound post was too long, the other was due to the instrument being dropped
A classical repair of this instrument involves taking the top off and fitting a sound post patch…quite expensive. The other option is to go through the top and fit cleats either side of the sound post.
To manage expectation here is a crack repair that was less clean, when the instrument broke it was cross grain and some small splinters were lost. Re alignment of the crack wasn’t perfect.
