I agree with this. My situation is completely same. Connected and worked fine at first, but after used 1G(checked from the website which is shown in the package) just 6 days, means not massive use, 100M/day1, 25M/Day2, 0.3M?day3, ...., the speed decreased to 125kbps, checked by some website. It was cheap, but ...... need to say.
My parents visited me this summer. I bought this for my mama, so that she and my dad could call me by skype when I was going to work. She used my wifi at home, and I do not know how much M or G can be used a day.
Follow instructions exactly and works first time but very slow download and upload on both LTE & 3G (ie 100kbps). Hotel WiFi was usually faster. Only used 1GB out of 3.5GB over 2 weeks using maps and mail. Too slow for even youtube.