Those two devices you pointed out serve two different purposes.
The Froggit is a logging device that has a way to see the current and historical trend with graphs and tables and is accessible via a mobile device. No app needed for the Froggit. You just open the browser and go to Ecowitt.net. You can save a home screen shortcut icon to make it seem like it is a an app you are launching and it will take you directly there. I'm familiar with this product and I think it will serve your needs. This requires WiFi and Internet access to upload to Ecowitt.net. This system is capable of being expanded to a full weather station if you want. Or you can just add a bunch of sensors. You should also check out Ecowitt.com to see this device called the GW1000 as it is the same thing. Basically Ecowitt is the inhouse brand of Fine Offset that actually makes this device. With Ecowitt you can custom order the number of sensors you want in your order. You can have up to 8 temperature/humidity sensors WH31 (plus an additional one if you could the one built into the gateway device. Actually you can have yet another one if you add the WH32 (only one of these) but this one is intended for outdoor use (you still need to protect it so I recommend the RS-00001 shield for it). With Ecowitt.net you can set alarm conditions.
- Fine Offset - company that makes the Froggit and Ecowitt hardware
- Froggit - one of many resellers of Fine Offset hardware - seems to be one of Europe's resellers
- Ecowitt - the inhouse brand from Fine Offset (offers the most amount of customization in sensor options) They ship worldwide
- Ecowitt.com - is the company's website where you can see their products (you can customize so do contact them directly)
- Ecowitt.net - is the online service that the hardware uploads to to see your data (current conditions, graphs, tables and set alarms), most recent Fine Offset stations upload to Ecowitt.net with notable exception Ambient's hardware as they have their own similar online service.
- Ambient Weather - Probably the largest of the Fine Offset resellers, but they only sell to the US market.
The second device you referenced, Xiaomi, is a device that you would use for home automation. I'm not certain that it has any decent historical reporting capability, as it seems to me that it probably has none. This is the sort of device that you use for alerting to certain conditions or you set as part of a greater home automation system where sensors can be triggers for lights or alarms or email notifications and and such. Probably similar to what you get from Samsung SmartThings. Although If you needed home automation stuff I think I'd recommend Samsung SmartThings instead of Xiaomi. Hubitat is also another notable home automation solution because the automation control happens locally without the cloud.
