I use Electrum wallet on both mobile and PC and it works pretty well if you are not planning to hold a lot of funds in it. It is safe and secure as long as you keep your devices away from phishing attacks, malware, and other such stuff that could get access to your device and then get into the wallet software that you are using.
It's better if you use two different wallets with Electrum wallet software, one wallet for your PC and another wallet for your mobile phone/ device. Don't use a same wallet on both PC and mobile device because if one of two devices is compromised, you will lose all bitcoins.
When you are using online wallets either on your mobile phone or personal computer, you need to make sure that you don't download or install untrustworthy applications or anything, don't click unknown links, don't give access to your device to any app even if it's for a short period because these things can compromise the security of your device and funds.
The warning is more. Verify your Electrum wallet too, before using.
[GUIDE] How to Safely Download and Verify ElectrumThe paranoid user's security guide for using Electrum safely.