The best part about tech cello was that they were able to implement all of our features within two weeks, whereas other companies took months or years! There are some minor bugs here and there but I believe it's because we're new customers so maybe things will get better once they've had time working together? We have been using them since January 2018 and haven't found anything negative yet - everyone at their office has been very helpful from start to finish (initial consultation through implementation).
They really do go above & beyond what you would expect when dealing with such large organisations like ours.