I don't know this Company, SOG, so I can't answer your question. There are plenty of good firms out there offering this sort of remedial service. There are also a lot of chancers, employing "surveyors" to advise ....... beware.
1 A great deal of "damp" is, in fact, condensation, where different solutions are needed.
2 If they're drilling from outside, I guess it's chemical damp-proof course injection. Depending on the construction of the wall, it can be very successful. In other cases it can be an utter waste of money.
3 As for avoiding interior plastering ........... if it is rising, then the plaster is already contaminated with various salts that will continue to show.
I'd really like to know what the wall is made of; how thick; how old; which room; also, is the outside ground level higher than the inside?
100 years old...... I guess it's 9" solid brick construction.