The Durfon 1X will work just fine. I use the analog version with a port on the gateways I install for the rooms as the SIP version is more expensive and the clients like spending less. I have about 16 installed. They are predominantly in hotels where the front desk is manned by single person, but they sometimes have to leave the desk to respond to a situation and then take the phone with them. The hotels are minimally two stories (most are more), with over 100 rooms and the phone will cover far more than the hotel property. For fun, I took a handset to dinner at a local cafe some 1/2 mile away and was still able to reach the base back at the hotel without issue. Of course, the positioning of the base and other factors come into play with regard to range, but there is no other phone on the market in the US with this ranger. They are quite durable as they are ruggedized, so they are able to take some abuse, but they are not indestructible and given their cost, should be given some care. They come with a stubby and a whip antenna, the whip being the better for max range. You may also need to order some spare batteries as like all rechargeable batteries, they do not last forever.
These are neither DECT or Wi-Fi as they operate in the 900Mhz range which is what contributes to their ability to be able to penetrate obstacles better than the other devices. They have a max output of 708mw.
While I have not used the SIP version, I have no doubt that it will work just fine. There is ONE THING you should do and that is to go to their site and download both the SIP and analog manuals. You should check to see how transfers and the other call control functions are accomplished in each assume there may be a need. If using analog, you want to be certain that you can match the method to the device that it will connected to. Some ATA devices may use a hook-flash and then a dial code whereas others not. Using what I do, transfers are able to be done, The SIP phone user manual indicates that transfers can be done as well, but the wording used makes it seem as though it may only be possible between the SIP handsets. I suspect this may not be the case, but rather how the manual was written not taking into account other PBX connected endpoints, but a note to their support should clear that up quickly.
The 1X in the analog or SIP is the better phone in the lineup for both range and durability.
The attached will give you some idea of what the phone will do, but still the manual will provide as more as will their support group.
https://www.engeniustech.com/resources/DuraFon-SIP Presentation.pdf