I had a number of packs rebuilt by MTO. Was $25 to rebuild those certain size packs so to me it was cheaper to get them rebuilt than to replace all of them.
First thing I did was open & inspect them. While they work fine & I no longer have unbalancing issues, I personally did not like the quality of the work so I won’t ever go to them again if the situation came up again. YMMV. But they are functional for daily work use so I can't complain overall. If there is a next time, I'll invest in rebuilding them myself.
For larger packs it's definitely not worth sending them out to pay for rebuilding. Only if they are uncommon battery packs and/or never go on sale.