Whilst switched mode suppliers are seen by some a universal panecea for power supply applications, as has been mentioned there are some applications where linear supplies are far better.
One such application is in powering RF modules, receivers in particular, have a read of this;
Note the very significant effect the switcher in the power bank has on the receivers RF sensitivity. I have seen the same effect using typical 'cheap' switchers that you will find on eBay.
Whilst its possible to design EMI quite switchers, all to often people are more concerned with 'cheap'.
Unless you are prepared to spend a while testing and analysing the effect of a switcher supply on an RF receiver, if you want 'cheap' then stick to linear supplies.